132 Chlorophyceae 



of the pyrenoid consist of a protein crystalloid but that the envelope is also 

 of a protein nature. 



In the Chlorophyceae the stored product of photosynthetic activity is for 

 the most part starch. The exceptions to this are the Heterokonta 1 , in 

 which the reserve is always a fatty oil, several of the larger species of 

 Mesotwnium in the DesmidiaceaB, certain species of Conochsste, Protococcus, 

 Asterococcus, Schizochlamys, etc. ; and the genus Vaucheria, in which oil is 

 stored instead of starch. Oil globules also frequently appear in a number 

 of other Green Alga? in the late autumn. In the genus Trentepohlia oil may 

 be stored in considerable quantity, and there is frequently dissolved in it 

 a red or orange-red pigment which is one of the carotins. 



Some of the genera of the Chlorophycea?, belonging to the Chsetopeltidacese, 

 Aphanocha?tacea>, Coleocha?tacea?, and (Edogoniacese, possess either hairs or 

 bristles, which may be direct outgrowths of the cell-wall, as in the bristles 

 of Ch^tosphtvridium, Conochsste, or Aplianoch&te, or finely attenuated, 

 setigerous branches, as in various members of the Chaetophoracese. In 

 Bulboch&te the bristles originate as tubular outgrowths from the apical 

 region of the cells, and possess a hollow, swollen base. In Coleoch&te the 

 delicate bristles are conspicuously sheathed at the base. 



In those genera in which the thallus is permanently or temporarily 

 attached there are often developed rhizoid-like organs of attachment, which 

 are known as hold-fasts (or haptera). Except in the Cladophoracea?, Ulvacea?, 

 Trentepohliacea?, Siphonales and Siphonocladiales, these hold-fasts are, how- 

 ever, for the most part, only developed on young plants. 



MULTIPLICATION occurs in the unicellular forms by cell-division 

 (Desmidiacea? and many Protococcales), and in some of the filamentous 

 genera by the fragmentation of the filament (many of the Zygriemacese), 

 or by the detachment of smaller or larger portions of the thallus. The 

 last-mentioned method, which is really a proliferation of the thallus, is well 

 shown in the genus Caulerpa, and to a less extent in Monostroma and 

 Prasiola. 



Vegetative propagation may also take place by gemmw (which have also 

 been termed ' cysts '). These are frequently unicellular, or 2 3-celled, and 

 are mostly formed in the autumn as a means of surviving the winter in 

 a vegetative condition. They occur only in a few Green Alga-, but are 

 known in the Zygnemacea?, Ulotrichacea?, and Cladophoracea? (in which they 

 are cmnocysts) ; and in the Vaucheriacete, also, special short segments of the 

 coenocytes are often cut off for the same purpose. The walls of the gemma- 

 cells are generally of considerable thickness. 



ASEXUAL REPRODUCTION by zoogonidia (or, as they are commonly termed, 

 ' zoospores ') is general throughout the Green Alga^, although there is a 



