REJUVENESCENCE IN NATURE. 137 



the same generation (that is the first-cousin-cells) differ 

 from each other. The first condition is of especial im- 

 portance in regard to the development of the organic 

 differences in vegetative structure, since on it depends 

 the apical growth and the ramification of many-celled 

 plants; on the latter depends, among other things, a 

 duplicity of fructification, occurring even in the lowest 

 groups of the Vegetable kingdom, and which we shall 

 here, in the first place, briefly examine. Numerous 

 Algae produce two (or sometimes even three) kinds of 

 reproductive cells, either two kinds of moving or motion- 

 less gonidia, or gonidia and spores, or, lastly, two kinds 

 of spores, which last can also occur in the higher groups 

 of the Cryptogamia. Probably this phenomenon is more 

 generally diffused among the Algae than can be accurately 

 demonstrated at present ; therefore when I mention many 

 doubtful cases here, it is with the express purpose of 

 directing attention to an object deserving of further 

 investigation. 



Among the examples of plants with two kinds of moving 

 germ-cells, large (macrogonidid] and small (tnicrogonidid) 

 the Water-net (Hydrodictyon) already mentioned above, 

 is especially worthy of mention. The unicellular indi- 

 viduals of this Alga, hitherto incorrectly arranged with 

 the Zygnemaceae,* are united in their earliest stages into a 

 colony, forming a bag- shaped net. All the cells of such a 

 net are sister-cells, for they all originate in one and the 

 same mother-cell, but they do not all behave alike when 

 fructification commences. In certain cells are formed 

 somewhat larger and less numerous gonidia (according to 

 the size of the mother-cell, 7000 to 20,000), in other cells 

 of the same net somewhat smaller and more numerous 

 gonidia (30,000 to 100,000). Only the former (the 

 macrogonidia) form a new net, which they do after a short 

 tremulous movement (lasting about half an hour), without 

 leaving the mother-cell, by uniting together into a 

 daughter-net, which is gradually set free by the solution of 



* Kiitziug, 'Species Algarura' (18i9), p. 448. 



