Sterile Technique and Agar Culture/33 said to be sectoring. A sector is defined solely in contrast to the surrounding, predominant mycelia. There are two major classes of mycelial sectors: rhizomorphic (strandy) and tomentose (cottony). Also, an intermediate type of mycelium occurs which grows linearly (longitudinally radial) hut does not have twisted strands of interwoven hyphae that characterize the rhizomorphic kind. Rhizomorphic mycelium is more apt to produce primordia. Linear mycelium can also produce abundant primordia but this usually occurs soon after it forms rhizomorphs. Keep in mind, however, that characteristics of fruiting mycelium are often species specific and may not conform precisely to the categories outlined here. In a dish That is largely covered with a cottony mycelia, a fan of strandy myceiia would be called a rhizomorphic sector, and vice versa. Sectors are common in mushroom culture and although little is known as to their cause or function, it is clear that genetics, nutrition and age of the mycelium play important roles. According to Stoller (1962) the growth of fluffy sectors is encouraged by broken and exploded kernels which increase the availability of starch in the spawn media. Working with Agaricus brunnescens, Stoller noted that although mycelial growth is faster at high pH levels (7.5) than at slightly acid pH levels (6.5), sectoring is more frequent. He found that sectors on grain could be re-
Figure 37 Psilocybe cubensis mycelia with cottony and rhizomorphic sectors. Note that primordia form abundantly on rhizomorphic mycelium but not on the cottony type.