200 ADVANCED TYPE OF REPRODUCTION 



case of Ulothrix. The contents of the gametospore is extruded 

 through the ruptured wall as a delicate sac and then divides, 

 forming four zoospores which produce new plants (Fig. Ii6, C-G) 

 — thus we see again an illustration of the peculiar nature of the 

 gametospore as in Spirogyra and Ulothrix. The question will 

 naturally arise as to the force that brings these and other gametes 

 together. The frequently observed aggregation or sw^arming of 

 the male gametes about the females renders probable the view 

 that some substances, as organic acids, etc., are developed in the 

 gametes that serve to draw them together whenever they come 

 within a certain distance of each other. 



The consideration of Coleochaete, a plant of the same order as 

 Ulothrix, has been deferred to this point because it presents 

 several interesting departures from previous types which indi- 

 cate that a higher point has been attained in some respects by 

 this plant than by any other of the green algae. The filaments of 

 Coleochaete have a pronounced apical growth and are usually 

 associated together in a radiate manner, forming small discs or 

 cushion-like masses on the stems and leaves of water plants (Fig. 

 117). The advance of this type is indicated not only by the 

 localization of growth at definite points, but also by the formation 

 of the zoospores and gametes in definite regions, i. e., in special 

 cells which are usually located at the end of the filaments. The 

 zoospores are produced singly from such cells, and from smaller 

 pear-shaped cells single male gametes are formed. The female 

 gametes are developed singly in large flask-shaped cells, access 

 to which is afforded by an opening that appears at the end of 

 the long neck of the flask (Fig. 118, A). The gametospore de- 

 velops a cell wall and becomes enveloped by the adjoining cells 

 of the filaments (Fig. 118, 5). In this condition the winter is 

 passed and in the spring it germinates, forming neither a plant 

 like the parent type nor zoospores as in Ulothrix and Oedogonium, 

 but instead, the gametospore forms a number of cells. This 

 growth ruptures the coat of the spore and finally from each cell a 

 rather irregular zoospore (Fig. 118, c) is derived that develops 

 into a small plant. The plants thus formed multiply solely by 

 zoospores until finally, after several generations, larger plants 



