BOTRYDIACE.E. 113 



of slightly coloured protoplasm. Theso zjospores conjugate in twos, 

 sometimes several together. They come in contact by their ciliated 

 ends, then come to touch laterally by the uncoloured portions, when 

 the fusion of the conjugating zoospores takes place, immediately after 

 which they present a cordate figure, and in the middle a colourless 

 vacuole. Finally, the isospore thus originating becomes globular, the 

 vacuole occupying the centre. 



If the zoospores be isolated before conjugation, they will in the end 

 break up, without presenting any products capable of germination. 



The zoospores originating from red spores have a different figure, 

 their posterior end being rounded, but they have otherwise the same 

 structure, and behave in the same manner as the others. The red 

 spores maintain their germinative power for years, but after two years 

 their zoospores are languid, and offer a parthenogenesis of a peculiar 

 kind. The red spores, if kept moist only, become nothing altered after 

 weeks, whilst the green, under these circumstances, may directly 

 germinate into vegetative plants. 



The isospores are at first globular, and capable of immediate germina- 

 tion. They also present resting stages, the original form becoming 

 modified. Soon after conjugation these are flattened, with irregular 

 lateral boundaries, which become on the following day hexagonal. The 

 membrane becomes thickened, and presents tuberculations at the 

 margin, but no secondary membrane is formed. Brought upon damp 

 earth, they soon become globular, and otherwise behave as ordinary 

 isospores. 



In order to distinguish that which appertains to the cycle of alterna- 

 tion of generations from the rest, the simple method is to start from the 

 fertilized germ, and see what are the modifications which are essential 

 in order to arrive again at the same reproductive process. In this case 

 we have the isospore it germinates produce the vegetative plant, 

 which needs neither to divide, nor produce a sexual zoospore, nor to 

 become an ordinary zoosporange it can directly produce spores. These 

 close the first generation. The second oospore generation occurs in the 

 germination of these spores in the form of sexual zoospores, which 

 directly lead to the formation of the isospore the limits of two genera- 

 tions. All the rest are but phenomena of adaptation. 



" Thus, in nature, the vegetative plants in spring almost all become 

 zoosporangia, and spread the growth over considerable areas. Zoospores 

 which fall into the water are not lost ; they acquire a double membrane, 

 and lie dormant until they chance mechanically to arrive on moist soil. 

 If drought sets in, the plasma retreats to the roots ; if the earth be 

 some time a little moist, the root cells become hypnospores, awaiting 

 the rain in order to develop multitudes of zoospores 5 but if the earth 

 becomes rapidly dried, the root cells remain unaltered, until a moistening 

 excites the formation of zoospores. A great many of the root cells can 

 manifestly accidentally reach the surface of the soil, and thus, according 

 to the state of the moisture of the earth or of the air, sometimes ger- 

 minate, sometimes become zoospores." All this in the spring. The hotter 

 months favour the formation of spores, but at that time only the 

 vegetative plants are mostly to be found, either undergoing cell division 

 or spore formation. They can also furnish uniciliate zoospores without 

 becoming modified into ordinary zoosporanges. 



Formation of ordinary zoospores may be accomplished in a fourfold 

 way 



1. From the vegetative plant. 



2. From the ordinary zoosporange, 



3. From the root cell. 



4. From the hypnosporange. 



