ON THE SAPROLEGNIE^. 187 



is able, without the assistance of any other organ, to produce a 

 new individual. Of this nature are the conidia of Empusa. It is 

 said to be sexual^ when two cells, developed expressly for the 

 purpose, combine, either by complete coalescence or by partial 

 intermingling of their contents, to produce a body out of which 

 one or more new individuals arise. But these two kinds of repro- 

 duction may occur in the same individual, or may be distributed 

 in different individuals, and in both cases the entire process of 

 development may be divided into two sharply separated stages. 

 At the termination of one stage sexual organs are formed ; by 

 their union the second stage of development is rendered possible, 

 and this closes with the production of asexual spores. Such a 

 course of development is termed, from the analogy of certain pro- 

 cesses in the animal kingdom, an " Alternation of Generation," 

 and is especially applicable when, in one or both stages of deve- 

 lopment, multiplication also takes place by conidia. 



As regards the structure and development of Saprolegnia^ there 

 is, first of all, the felted mass of mycelium common to all fungi. 

 From this grow filaments, called " hyphae," which are tubular, thin- 

 walled, and lined by finely-granular protoplasm. The ends of some 

 of the hyphae become enlarged to form the spore-cases, in which 

 protoplasm accumulates, and the cavity is shut off by a transverse 

 partition. In a short time, the protoplasm breaks up into little 

 spheroidal bodies, which form the spores, or rather zoospores, for 

 under certain circumstances they are actively locomotive, after the 

 fashion of many animalcules. When the zoospores are perfectly 

 developed, the apex of the spore-case, or " Zoosporangium," opens 

 and the zoospores are emitted. Each zoospore, as it leaves the 

 zoosporangium, is usually in active motion, being propelled by the 

 rapid lashing of two vibratile cilia, which are attached to one 

 point of its surface. After a few minutes it becomes quiescent, 

 and surrounds itself with an extremely delicate transparent coat. 

 But this repose is of very short duration, as it soon emerges from 

 its envelope, and moves about even more actively than before. It 

 has now an elongated, oval, or kidney shape, and has two cilia, 

 which proceed from one side of the oval. This second active 

 state may last for a day or two, but sooner or later the zoospore 

 comes to a state of rest, which is final, and then usually germinates. 



