The Architecture of the Sporophyte
The Architecture of the Sporophyte
The rise of the sporophyte in land plants demonstrates a marked evolution in the morphology and reproduction of plants. From early land plants, such as bryophytes, to angiosperms, the sporophyte has experienced incredible physical transformation. Our project seeks to literalize the changes in the architecture of the sporophyte and represent these biological phenomena through the architecture of the built human environment. Each photograph and its accompanying description detail the physical development of the sporophyte and relate the physical characteristics of plants with their architectural counterparts of the Harvard campus. We challenge our readers to apply the concepts behind the eventual dominance of the sporophyte in land plants to the structures and spaces that shape our daily lives.
Isaac C. Dayno ‘15 and Roland Yang ‘14 Harvard College April 2014 OEB 52 Final Project
The dock of Weld Boathouse, the border between the Charles River and the Harvard campus, where water meets land, hearkens to how freshwater algae gave rise to the earliest plants. At this critical juncture, we see early land plants diverging from their algal ancestors, and much like in their aquatic predecessors, the gametophytic form dominates their life cycle. The flatness of the dock mirrors the level of the boundary layer, a wet microsite where the earliest plants, unable to procure their own water, would have passively wicked moisture from their surroundings. These would also have relied on water to reproduce among their dominant gametophytic forms.
The bryophytes have the most complex gametophytes of land plants. Among them, we find the hornworts. Unable to pull water on their own and desiccation-tolerant, these plants lack vascular tissue. Hornworts elevate their sporophytes,indeterminate growths,thanks to an intercalary meristem at their base. Despite this raised position, the sporophyte remains anchored in the gametophyte, depending on it for water, minerals, and photosynthate. Outside of Boylston Hall and Widener Library, the base of the Harvard Bixi, a 18thcentury marble Chinese stele, calls to mind that very meristem, and the continual growth and persistence of the sporophyte, as long as its gametophyte counterpart continues to exist.
Another type of bryophytes, liverworts’ sporophytes are determinate, do not have stomata, are unbranched, and their spores mature before they are distributed into the environment. The gametophyte is still dominant, characterized by complex structures such as the antheridiophore and archegoniophore that elevate gamete-producing parts. On the other hand, the sporophyte is a simple structure dependent and borne out of this haploid The glass dome of the cupola of Rosovsky generation. Hall represents the archegoniophore, a specialized elevated axis of the maternal gametophyte. The metal latticework beneath the domes in turn symbolizes the sporophyte— composed of a foot, seta, and sporangium, where spores are mixed with elaters before dessication releases them to the wind.
True mosses exhibit determinate growth in their sporophytic axes, which emerge from the maternal gametophyte. Like their liverwort and hornwort cousins, the sporophyte of these plants grows with a foot in the maternal archegonium and still depends on the gametophyte for nutrition, through hydroids that are continuous with the maternal body.
The Stillman Gate Posts of Dunster House echo the elongated seta of the peristomate mosses, topped by the gametophytic calyptra that protects and limits the sporophytic capsule until the former ruptures. Under biphasic nutrition, this allows the sporophytic capsule to transpire and draw nutrients from the gametophyte, drying to eventually release its spores.
For the first time, the lycophytes mark the ascendancy of the sporophyte. Exhibiting dichotomously branching sporophytes with multiple sporangia, these plants grow strobili to disperse spores, while at the same branch points, roots grow down from the rhizomes. The gametophyte can be either terrestial or subterranean and is reduced to a bisexual form. Although diminutive, this gametophyte persists and can support multiple sporophytes during its life, relying on symbiosis with fungi to extract nutrients.
Much like the independent, autotrophic, and complex sporophytes in the lycophytes, the towers of Peabody Terrace rise from their own network of “rhizomes” and buried gametophytes—the ground-level and subterranean garages and living structures that anchor the towers in Brutalist architecture. The upper spires of the towers resemble the strobili of lycophytes, structures projected into the air like fertile microsporophylls. The different sizes of window elements also denote the introduction of heterospory, in which spores differ in size based on their sex.
The sporophyte has gained even more dominance in the monophyletic group of ferns. Generally homosporous, ferns exhibit a body plan that comprises a rhizome, an upright frond, and an associated root. The sporophyte—now vascular and free-living—places its sporangia in aggregations called sori on the abaxial surface (underside) of leaves. In the arms race between the gametophyte and the sporophyte, the fern gametophyte, although buried in the earth, is free-living and desiccation-tolerant, and able to produce generations of the shorter-living sporophyte (though they only produce one sex of gamete at a time, the female often being the larger).
The Towers of Leverett House, modernist interpretations of residential life at Harvard, mirror the morphology of ferns. The large windows represent the patterns of sori, while the casing of the ventilation systems on the roof and its distinctive structure echo the blade patterns of the sporophylls. Meanwhile, the Leverett Library (low building in the foreground) reflects the gametophyte—freeliving and giving rise to generations of tall, free-standing concrete sporophytes nearby.
The sporophyte has reached its true dominance in seed plants, posing radical changes to plant morphology. The microgametophyte has been severely reduced; as pollen, it now travels by air, to meet its female counterpart retained within the adult megasporangium of the adult sporophyte. The megagametophyte is retained in this megasporangium, producing the eggs that are fertilized in situ and create a seed. Once dispersed and germinated, the seed produces a new generation of adult, diploid sporophyte, and the life cycle continues.
tissue of the integument, the sunken concrete walls of Pusey encircle a growing megasporangium and megaspore, represented here by the earth and vegetation of the courtyard. Eventually, that megaspore will develop into a megagametophyte, which produces an egg that, when fertilized by the nuclei of incoming pollen, develops into an embryo. The tree growing in courtyard represents that embryo, and the mulch around it the endosperm that nourishes it.
The light walls of Apthorp House (overleaf ), contained but sprouting out of Adams’ cenThe courtyard of Pusey Library resonates tral courtyard, likewise mirror the endosporic with the retained nature of the gametophyte. development of the gametophyte, common Much like the surrounding adult sporophytic to most hetersporous vascular plants.
The gymnosperms represent another step in the superiority of the sporophyte. Literally “naked seed,” these plants use cones to disperse pollen and retain the megagametophyte for the development of the egg and the eventual fertilized seed. In some conifers, a family of gymnosperms, it may take a few years until the cone matures. One thing remains certain, however. The longevity of these trees, like some pines, attest to the incontestable place of the sporophyte in the gymnosperms’ reproductive and life processes.
The bells of St. Paul’s Church tower echo the exposed nature of gymnosperm reproductive structures—bells shaped like cones, open to the air, clappers like naked seeds. The sporophytic generation of pines are the longestliving organisms on the planet, with some specimens surviving for thousands of years. In the same way, the Italian Romanesque style of St. Paul’s has lasted over a millennium.
The angiosperms represent the final, major stage of plant evolution, and an unprecedented level of sophistication in the rise of the sporophyte. The ovule is doubly integumented; the megagametophyte has been severely reduced to seven cells and eight nuclei. Adult sporophytes reproduce by the hermaphroditic axes of flowers. Double fertilization of the egg and central cell nucleus creates a diploid embryo and a triploid endosperm respectively. And the carpel that contains these eventually matures into a fruit.
Like the fruit of angiosperms, Harvard’s rare books and manuscripts collection, Houghton Library, also encases its valuable contents in a brick carpel of its own. Books on shelves recall the marginal placentation of seeds in the carpel of some fruit—stacked on top of each other and lined in an orderly fashion. Like pollinators, students and researchers undergo screening by the guard, who acts much like the selective stigmatic surface, only allowing those who promise fruitful entry and inquiry...
Acknowledgements: We would like to thank Professors Elena Kramer and Tony Rockwell for their instruction, encouragement, and help with this project. We would also like to thank our Teaching Fellows, Dustin Haines and Yongjian ( John) Zhang for their weekly guidance and enthusiasm. Thank you all for showing us the beauty of botany! Credits: All photographs taken by the authors. All text jointly composed by authors. Designed by Roland Yang on InDesign, typeface Adobe Caslon. Published by Isaac C. Dayno on Issuu.