190 



MANUAL OF POISONOUS PLANTS 



/ I 



Fig. 32a. Lower figure, two views of diatom. 

 m lateral view; / upper view. Upper figure, a desmid 

 Closterium; chl — choroplastid. Charlotte M. King. 



1 or more spiral bands, depending upon the species ; nucleus is generally situated 

 in the central portion of the cell ; in the chlorophyll band occur what are known 

 as the pyrenoids ; reproduction both asexual, by the simple cutting off of the end 

 cell, and sexual, by conjugation through the union of two cells. 



ZYGNEMATACEAE 



Cells cylindrical, unbranched forming threads, chroiiiatophores present, in 



masses or spiral bands. 



Formation of zygospores. 

 CHLOROPHYCEAE 



Chlorophyll-green plants, occurring singly or in colonies, (threads or flat- 

 tened bodies) with one or more nuclei; reproduction asexual by producing 

 multilateral zoospores and aplanospores ; sexual by the copulation of zoogametes, 

 or spermatozoids and oospheres; the spores produce a new plant directly or 

 generally form swarm spores. Water net (Hydrodictyon reticulatum) , Pedias- 

 trum and Scenedesmus are common in fresh water; Pleurococcus is common on 

 trunks of trees. The Confervales contain the sea lettuce, Ulva latissima, which 

 is used as food, the Conferva with slender green filiaments common in fresh 

 water, the Cladophora fracta in fresh water. Cladophora is a common alga 

 and is quite rough to the touch, and may therefore easily be distinguished from 

 Spirogyra or Zygnema. The frond of Cladophora is branched with many- 



