CHRONIZOOSPOllES OF HYDRODICTYON. 57 



alga can resist a long desiccation admits of another interpre- 

 tation ; it may be explained^ indeed^ by the existence of par- 

 ticular germs, possessing those properties wrongly attributed* 

 by A^aucher to the plant itself. Now, it appears to me that 

 these germs are no other than the microgonidia of Hydrodic- 

 tyon, those zoospores (fig. 1, a) which, at a given moment, quit 

 the utricular cavity in which they have been formed, and 

 spread themselves outside in all directions. 



Their activity lasts only a few hours ; when it has ceased, 

 far from germinating directly, they become round (fig. 1, b, c), 

 and their tegument acquires the character of a resisting 

 membrane, of the nature of cellulose. In this transformed 

 condition the microgonidia resemble the little granules of 

 Protococcus, and are able to endure for many months a com- 

 plete desiccation, provided they are protected from the action 

 of light. The changes they undergo during this time are 

 inconsiderable; at the end of several months they are still 

 green or yellowish globules, measuring tt-J,-;, or -j-^ mm. 

 in diameter, and very much the same as they were after 

 their first transformation. 



If they are exposed, on the contrary, to the light during 

 their desiccation, the microzoospores wither and die, and can 

 never be recalled to life by any means. 



If they are plunged in water, whether exposed or not to 

 the light, they may be preserved for many weeks, and even 

 months, without any alteration. It is only after a consider- 

 able lapse of time, varjdug, no doubt, according to external 

 circumstances, but never under three months in my expe- 

 rience, that the submerged zoospores give the first signs of a 

 new vegetation. They then behave exactly like those which, 

 after having undergone a prolonged desiccation in the dark, 

 have been just remoistened. 



Then all these globular cells, so analogous in appearance 

 to Protococcus, begin to grow slowly. During four or five 

 months, at least according to my own observations, their 

 vegetation only consists in an augmentation of size, so that 

 at the end of that time they represent so many large green 

 or brownish-green cells, whose membrane possesses a very ap- 

 preciable thickness. Their endochrome, rich in green mat- 

 ter, has at the same time increased and thickened, and a 

 large granule may be distinguished in it from the commence- 

 ment, which appears to play the same physiological part as 

 that attributed by M. Braun to the amy Ion- cells of the adult 

 Hydrodictyon. In the enlarged zoospore, though still re- 

 taining the form of a Protococcus, a vacuole might be sup- 

 posed to occupy the centre of its cavity ; but, in reality, the 



