Protococcus, etc — continued. 



Sexual Stage — 



Fig. 7. Portion of Filament producing Zoospores, which are smaller and more numerous than the Zoogonidia, and only possess 

 two cilia. 



The Mother-cell, contains eight, sixteen, or more Zoospores. 



In conjugation, two zoospores come together sideways and fusion takes place from the pointed end backwards. 

 The united zoospores behave like a zoogonidium, lose their cilia and settle down. The result of conjugation is a 

 Zygospore. 

 Fig. 8. The Zygospore germinates and divides into a greater or smaller number of Zoogonidia, which reproduce the plant as 

 before. 

 Non-Conjugating Stage — 



Fig. 9. Portion of Filament with Zoospores that have not escaped, germinating directly. 



When Zoospores do not meet in conjugation, they produce new plants directly, but they are weak and often 

 perish. 

 Life History. — Ulothrix may give rise to Zoogonidia, which germinate and reproduce the plant; or it may give rise to Zoospores, 

 which conjugate and produce a Zygospore, from which, by division, numerous Zoogonidia arise to go through the ordinary 

 course; or the Zoospores directly produce a new plant. 

 With regard to the Conjugation of U. zonata, Professor Dodel-Port remarks: "The conjugation of U. zonata represents the 

 simplest form of the sexual process. The conjugatory cells are alike, and are not distinguishable in their essential features from the 

 non-sexual reproductive cells. If, for any reason, conjugation has not occurred, they behave just the same as the zoogonidia, incapable 

 of conjugation, and develop non-sexually. The act of conjugation may be delayed without injuring their power of reproduction Con- 

 jugation appears here merely as the result of a lucky accident, and we may therefore consider Ulothrix as a type of those lower forms 

 which show us the first beginnings of the sexual process in plants." 



Hydrodictyon. 



Hydrodictyon (Gr. hudor, water; diktuon, a net-work), or Water-net, is met with in clear ponds or flowing streams. It often 

 occurs in great masses and the meshes of the net may be distinguished by the naked eye. 



The net is composed of cells containing green coloured protoplasm, and united so as to form a beautiful pattern. The contents of 

 the cells may either break up into Zoogonidia or Zoospores. 



The Zoogonidia may form in a single cell to the number of 20,000, and these minute particles have a swarming motion for a short 

 time, then they arrange themselves into a netted pattern, by bringing their ends properly together. The mother-cell ruptures, setting free 

 the delicately formed net perfect in all its details. 



Fig. 10 a. A small portion of the old net — natural size. 



(A) A very small portion magnified, showing the individual cells forming each mesh. 



