94 



BOTANY 



spore, which germinates only after a considerable period of rest. 

 Much less commonly (e.g. Ulva), the zygote germinates immediately. 



The simpler forms of gametes closely resemble the non-sexual 

 zoospores, from which they have undoubtedly developed. Occa- 

 sionally gametes, males as well as females, have been observed to 

 germinate without fecundation. This phenomenon is known as 

 Parthenogenesis. 



Certain groups of Green Algae, e.g. Volvocacese, still exhibit all 

 grades of development of the gametes, from uon-sexual zoospores to 

 perfectly differentiated spermatozoids and eggs. The latter finally 

 lose the power of movement, and remain within the mother-cell 

 (Oogonium), where they are fertilized by the small active sperm ato- 

 zoid. 



B 



FIG. 65. A, Oonium pectorale (X 450). B, a single cell of Gonium (X 800) ; 

 cl, chloroplast, with pyrenoid; n, nucleus; v, one of the contractile vacuoles; 

 e, eye-spot. C, Pleodorina Californica (X 75) ; the arrow indicates the forward 

 pole of the colony. D, three stages in the division of a gonidium. (D, after SHAW.) 



Classification of Chlorophyceae 



The Chlorophycese may be divided into the following six orders : 

 /. Volvocacece ; II. Protococcoidece ; III. Confervoidece ; IV. Con- 

 jugates ; V. Siphonece ; VI. Characece. Of these, the first three 



