126 



Minnesota Plant Life. 



variety of moss in Minnesota the stem is erect and there are but 

 two rows of leaves, each with a peculiar crest on its mid-rib. 

 When, on the other hand, moss stems are prostrate in habit 

 there is commonly something in their leaf-arrangement or in 

 their structure which indicates that they were not always pros- 

 trate but have adopted this position for some peculiar reason. 

 But among the "scale-mosses" those liverworts which bear 

 leaves in two rows there is nothing in the structure to suggest 

 that they ever maintained an erect position. Therefore, it is 

 possible to make this general distinction between mosses and 

 liverworts; that liverworts are essentially 

 prostrate plants and that mosses are essen- 

 tially erect plants in some of which the 

 prostrate habit of growth has been second- 

 arily resumed. 



Of whatever sort the plant-body may be 

 in the second-stage, it is always character- 

 ized by a variety of functions, of which the 

 breeding-function may be regarded as the 

 most important and secondary to that the 

 nutritive. When mosses are about to breed 

 they produce, in some species upon the 

 same plant, in others upon neighboring 

 plants organs of two sorts. The male 

 structures are commonly ovoid-cylindrical 

 in shape, situated sometimes in little clus- FIG. 4i. The c 

 ters at the ends of stems and surrounded 

 by leaves of slightly different color, more 

 purplish, yellowish, or reddish than the 

 ordinary leaf. Along with these bodies, 



standing on their short stalks, there are ordinarily developed 

 glandular hairs which serve to keep them moist by retaining a 

 little water in their vicinity. Each ovoid organ consists of a 

 layer of cells surrounding a central mass of small cells, several 

 thousand in number. Each one of the small cells is capable of 

 producing from the living substance of its interior, a single sper- 

 matozoid. When the whole organ is ripe, the end opposite the 

 stalk opens, separates or dissolves and the cells of the interior 

 are squeezed out. Their walls liquify and a horde of sperm- 



spermary of a moss, 

 much magnified, and 

 two spermatozoids, very 

 highly magnified. After 

 Atkinson. 



