iS 



A TEXT-BOOK OF BOTANY. 



ular or Brownian movement. Reproduction is either by simple 

 division or by the union of two Desmids. In the latter case the 

 contents of each flow together into a connecting tube formed by 

 the union of the two Desmids, the resultant mass rounding off to 

 form a zygospore. 



I'M.. 8. Forms of Desmids in longitudinal view and transverse section. A, Meso- 



tcenium i-raunn; B. A >n yimi,-rn,i \<>rden^kii>ldii; C. Penium digitus; D, Cylindrocystis crassa; 



E, C 'lustcrium mnilif>-rum; F , Spimt.inia muscicola; G, Pleurotcenium trabecula; H, a Docid- 



ntm {minium; H;i'. D. dilatutum. From Wille in Engler and Piantl's "Die Naturlichen 



inzenfamilien." 



Spirogyra. Another one of the common Green Algae is 

 Spinujyni ( \ : ig. <j), one of the pond-scums, which in the spring 

 forms floating ^reen masses on ponds and shallow water. The 

 plant-body consists of a chain of cylindrical cells forming long 

 threads or filaments. The- transverse walls are sometimes pecu- 

 liarly thickened. The chromatophores occur in one or more spiral 



