56 PRINGSHEIM, ON THE 



curious phenomenon satisfactorily. M. A. Braun Avas the 

 first to recognise the precise manner in which this intestine 

 generation of new plants takes place ; and he also first noted 

 the existence in Hydroclictyon of two kinds of zoospores, dif- 

 fering in size and produced in distinct utricles. He asserts 

 that the largest, described by him as macrogoniclia, are 

 specially those which unite into a network in the cellular 

 cavity where they are born ; whilst the others, on the con- 

 trary, the microgonidia more particularly, deserve the name of 

 zoospores ; they escape from the generative cell after it is 

 broken up, and it is above all when outside it, that they 

 move about with vivacity, in order to disperse themselves in all 

 directions. M. Braun supposes that these zoospores, when 

 they have become motionless, take the globular form of Proto- 

 coccus ; that they live some time longer without perceptible 

 growth, and perish at last without multiplying themselves in 

 any manner. 



After these observations, the history of the development of 

 Hydrodictyon might be considered to be perfectly under- 

 stood, at all events as much so as that of many other alya 

 in which the germination of the reproductive bodies had been 

 proved. According to the idea held at that time of the in- 

 ferior cryptogamic plants, the cycle of their existence was sup- 

 posed to be complete or thoroughly known, from the moment 

 a mode of propagation was discovered, whatever it might 

 be, by which the preservation of the species was assured in 

 itself; biit since our knowledge has been enriched by the 

 discovery of sexuality in the Confervse, and nobody can be 

 ignorant of the remarkable succession of abnormal or unex- 

 pected phenomena brought to light every day by the study of 

 different kinds of zoospores, we can no longer believe in the 

 apparent simplicity or uniformity of the development of the 

 inferior Cryptogamia, but are incited to try and bridge over 

 some of the too evident gaps in their history. With regard 

 to Hydrodictyon, another consideration, cominon alike to 

 many other fresh water alga, might long ago have led to the 

 supposition that its reproduction could hardly be solely 

 attained by the intra-utrieular networks. Many observers 

 Avill, doubtless, have remarked that in the isolated ditches 

 where this plant usually lives, it perpetuates and renews itself 

 indefinitely, in spite of the temporary draining of the water, 

 and the more or less prolonged desiccation thus caused. The 

 smallest experience will suffice to refute the opinion of 

 Vaucher, that Hydrodictyon can be entirely dried up without 

 perishing; an opinion, indeed, which it appears to me was 

 not founded on any accurate experiments. The fact that this 



