232 



THE POPULAR SCIENCE MONTHLY. 



The movements to which reference is here made belong in most 

 cases to a part rather than to the whole of a plant ; in some cases, 

 however, we find the whole organism endowed with spontaneous motion 

 of a very remarkable character. An instance of this occurs in the case 

 of the regular undulating motion, exceedingly similar to that of some 

 of the lower animals, characteristic of a class of Algae hence called 

 Oseillatoriae. The mode of reproduction of the Algae, the lowest class 

 of th.3 vegetable kingdom, to which the sea-weeds and the fresh-water 

 confervae belong, is often obscure, and in some cases different distinct 

 processes exist in the same species. In certain fresh-water Algae, repro- 

 duction takes place by the formation of "Zoospores" (Fig. 1), which 

 are the results of the separation and isolation of the protoplasmic con- 

 tents of certain special cells. According to the observations of M. 

 Thuret, who has paid great attention to this subject, these zoospores, 

 which are of extreme minuteness, are ovoid in form, and are furnished, 

 either over their whole circumference or toward one extremity, with 

 very fine cilia, varying from two to a large number. As soon as these 

 minute bodies free themselves from the cell in which they are enclosed, 

 the cilia begin to vibrate with great rapidity, the vibration being ac- 

 companied by a movement of rotation of the bodies themselves on 

 their axis, occasioned apparently by rapid and spontaneous contrac- 

 tions ; the result being a quick motion of the body through the water 

 undistinguishable, in fact, from that of some of the lower forms of 



Fig. 2. 



Fig 1. 



M&, 



animal life continuing for a period varying from half an hour to 

 several hours, at the expiration of which they settle down, reassume 

 the characters of ordinary vegetable cells, lose their cilia, and give 

 rise, by cell-division, to new individuals resembling the parent-plant. 

 Those zoospores which are furnished with cilia at one extremity only, 

 direct that extremity, which is destitute of chlorophyll or green color- 

 ing-matter, toward the light. Closely resembling these zoospores are 

 the "spermatozoa" of the higher orders of cryptogamic plants, ferns, 

 equisetums, and mosses. These bodies (Fig. 2) are produced in the an- 

 theridia or male organs, again by a modification of the protoplasmic 

 cell-contents; they are filiform bodies of various forms, mostly pre- 

 senting one or more spiral curves, and furnished with vibratile cilia. 

 When released from the parent-cells, they move about with great ac- 



