CHARACTERISTICS OF THE TRUE FUNGI 45 



aquatic medium, and the success of the process of fertilization depends 

 on the presence of free water. Such fungi form a subclass of EUMY- 

 CETES, the PHYCOMYCETES. 



The vegetative organs of fungi are concerned with the absorption 

 of food, the assimilation of the food and in the nutrition of the organs 

 of fructification which together form the reproductive system. That 

 the student may appreciate the morphology of the vegetative organs of 

 the fungi, three examples from widely divergent orders will be chosen 

 by way of illustration. A common mould is Mucor mucedo which 

 appears on horse manure. If a spore of this fungus is placed in a nutri- 

 tive medium, its wall breaks and there protrudes a germ tube rich in 

 protoplasmic contents (Fig. 13, h). This germ tube grows in length 

 into an hypha without the development of partition walls dividing it 

 into shorter cells. This hypha branches and rebranches in its growth 

 over the nutrient substratum spreading in all directions, if unimpeded 

 by other organisms growing on the same food substance. The ultimate 

 branches of this mycelium, which is throughout unicellular, are much 

 attenuated, fine hyphse representing the end ramifications of larger and 

 coarser hyphae nearer the point of origin of the whole mycelium (Fig. 

 13). The finest hyphae usually enter the substratum, while the coarser, 

 stronger hyphae form a cobwebby mass over its surface. We can 

 distinguish therefore the feeding hyphae, which are rhizoidal hyphae, 

 and the aerial hyphae in which probably the metabolic changes are 

 most active where the mycelium is in open contact with the air. Later, 

 when the mycelium is well established on the nutrient substratum, 

 erect vertical hyphae appear at indefinite points on the larger aerial 

 hyphae. These are the fruiting hyphae, or sporangiophores, which 

 ultimately cut off a terminal cell which becomes the sporangium, or case, 

 in which the reproductive cells or spores are formed, while the end of 

 the sporangiophore projects into the interior of the sporangium as a 

 columella (Fig. 13, /). 



The common green mould, Penicillium glaucum, may be taken as the 

 second illustration (Fig. 14). If we sow a spore on nutrient agar in a 

 Petri dish after a few hours the spore swells and there emerges a germ 

 tube which at first is undivided by a partition wall. Later, as the older 

 hyphae branch to form new ramifications, cross-partitions are formed 

 which divide the mycelium into short cells, so that in that respect the 

 mycelium of PeniciUhim differs from that of Mucor. The hyphal 



