520 Minnesota Plant Life. 



Spermatozoids are typically small motile cells provided with 

 two or more swimming lashes, by means of which they can 

 progress in the water. The sperms of the water silk and some 

 of its relations are pear-shaped, with the lashes on the smaller 

 end. Those of the brown seaweeds are somew hat pointed, with 

 the lashes on one side. Those of mosses, ferns and higher 

 plants are commonly more or less corkscrew-shaped. In mosses 

 and club-mosses two swimming lashes are formed, but in ferns, 

 cycads and some other higher plants that have been studied the 

 number of lashes is greater. In two high types of plants the 

 lashes seem to have been lost, viz., in red algae and in most 

 flowering plants. The size of spermatozoids is almost inva- 

 riably below the limit of unaided vision, but sperms of cycads are 

 plainly \'isible, without the assistance of a microscope, as tiny 

 specks. As produced in some of the algae, sperms contain 

 leaf-green and considerable living substance in addition to the 

 portion termed the nucleus; but in brown and red algae and 

 in flowering" plants the substance is principally nuclear. Unlike 

 many spores, spermatozoids are not formed as superficial cells, 

 but originate from the divisions internally of mother-cells. 

 Sometimes, as in the sphere-alga, enormous numbers arise from 

 a single mother-cell, but more commonly only one sperm de- 

 velops in each. The mother-cells may be superficial and aggre- 

 gated, possibly, in exposed clusters, as among brown and red 

 algae. On the other hand they may form the core of a solid 

 organ, the spcniiary, as in mosses, liverworts and ferns. In 

 the cone-headed liverwort, for example, thousands of sperm- 

 mother-cells arise in each microscopic melon-shaped spermary, 

 and, in the course of its life, a male cone-headed liverwort 

 produces millions of such cells. In higher plants the males 

 become greatly diminished in size and the number of sper- 

 matozoids that one can produce during its life is reduced to a 

 score or less in water-ferns, to four in the (juillwori, and to iwo 

 in most seed-producing plants. 



Distribution of spermatozoids. Each spermatozoid is care- 

 fully constructed within its mother-cell, and when the latter, 

 by solution of its wall, opens to release the tiny male cell, this, 

 in moss or fern types, swims rapidly aw a)', it is carried in red 

 algae t\pes b\' water currents, and is libcraicd dirccil\' beside 



