124 APPENDIX. 



In Liquids. — A floating network of fibrils, with a very few twigs 

 raised above the surface, on each of which is borne a sporangium. 



Microscopically. ^^^OTzxigwiva, when ripe, seen to be delicately 

 furred on surface ; when still unripe, it is quite smooth. Spores 

 densely packed within, can only be seen by bursting sporangium. 

 Pigment amongst spores as black powder, and in texture of capsule, 

 not however in spores themselves. Mycelium consists of greatly 

 elongated cells, the septa between which can be seen. 



M. LiCHTHEiMii. — Like M. mucedo in all respects, except that its 

 growth is not so luxuriant, the mycelium is more delicate, and its 

 fibrils more attenuated. The sporangia are smaller than in M. mucedo, 

 and are not pigmented. (Fig. 23, p. 64.) 



M. STOLONIFER. — Exactly like M. mucedo, except that the mycelium 

 grows in the manner of stolons, shooting into air, and then bending 

 down, and again entering the nutrient soil. Sporangia black, as in 

 M. mucedo. 



Salmon fungus. — Saprolegniaferax, an aquatic fungus, which grows 

 most readily on dead flies or dead fish, especially if they are placed 

 in running water. It forms a delicate cloud-like mass (an aquatic 

 mucor) on the surface, and grows very rapidly. Under the micro- 

 scope are seen tubular branching hyphse, the protoplasmic contents 

 of which are coarsely granular. Reproductive organs elongated, club- 

 shaped zoosporangia, which open laterally or terminally, and rounded 

 oogonia, in which are oospores. The zoospores which escape from 

 the zoosporangia are usually ciliated or tailed. 



The growth does not appear to pass deeply into the tissue of its 

 host. 



Closely allied to this species are the Achlya polyandra and Achlya 

 apiculata. 



GENUS PENOSPORA. 



Penospora infestans is the most important member of this group, 

 which contains nearly forty known species. It is the cause of the 

 potato disease. The full-grown fungus consists of a branched my- 

 celium 0-005 millimetre in thickness, upon the terminal twigs of 

 which oval conidia are supported. The mycelium and conidia pro- 

 duce together a thin grey pellicle, which adheres firmly to the diseased 

 parts of the plant, notably the green stems and the under surface of 

 the leaves. The diseased portions of the plant itself become withered 

 and brown. The mycelium spreads far and wide through the plant, 

 and soon reaches the tubers. In this position it remains during the 

 winter, and, growing up within the young shoots of the new plant, 

 develops once more its mature conidia upon the free surfaces of its 

 host. The spores, falling to the ground, become actively moving 

 swarm-spores, and attack other plants with which they come in 



