Minnesota Plant Life. 521 



the egg in seed-plant types ; for in them the pollen-tube con- 

 taining the sperms grows into the immediate vicinity of the 

 eggs produced by the female of the species. In its movements 

 the spermatozoid is guided by chemical stimuli. The duration 

 of its locomotion varies in different forms, but is rarely known 

 to exceed a few hours. 



Production of eggs. Plant eggs occur in all species that 

 produce sperms, for the two kinds of cells are complementary. 

 In lower forms eggs may be motile and very much like sperms 

 in appearance. They are distinguished, however, by tiring 

 more quickly or by their slightly larger size. Typically, how- 

 ever, eggs have no swimming lashes and are quiet, passive cells, 

 containing leaf-green bodies or their rudiments, in such plants 

 as produce leaf-green ; and they are much larger than the sper- 

 matozoids of their species. Yet plant eggs never reach the 

 size of similar cells in animals, and the largest, among which 

 should be counted the eggs of pine trees, are little ovoid, whitish 

 bodies that may be dissected out of the rudimentary seed where 

 the female lives and produces them, and may be picked up on 

 a needle point for examination by the unaided eye. Most plant 

 eggs are microscopic. 



Eggs, like sperms, may be produced in mother-cells, some- 

 times several from each, but more often only one. In the 

 sphere-alga a row of almost spherical eggs is produced in each 

 of certain tubular cells of the filamentous plant-body. But occa- 

 sionally eggs arise as the terminal cells of filaments, as in bass- 

 weeds, where they are protected by a sheathing layer. Since 

 the egg is a very important cell in the plant economy, it is 

 protected from harm, in all higher plants, by surrounding cells ; 

 and thus in the series of plants extending from the liverworts 

 to the pines, eggs arise in fiask-shaped organs, one egg at the 

 bottom of each flask. Clusters of such microscopic flasks are 

 found at the end of the stem of a female moss plant, on the 

 under side of fern sexual plants, and embedded in the surface 

 of the enclosed female plant of rudimentary pine seeds. The 

 egg organ serves the double function, in such plants, of pro- 

 ducing the egg and protecting the young embryo during its 

 early stages. 



In a few plants eggs are ejected from the body of the female, 

 as among many animals — for example, fish; but generally the 



