512 Minnesota Plant Life. 



such as tlie mosses, propagation is abuiKlanl; in others, such 

 as the mustards, it is rare or unusual. Special propagative 

 bodies, like the gemnicC of the umbrella-liverwort, the bulbils 

 of ferns or of tiger-lilies, and the brood-cells of many mosses and 

 fungi are not uncommon. When they are one-celled they are 

 difficult to distinguish from true spores. 



Of important propagative organs among higher plants should 

 be mentioned the rootstocks, tubers, l)ulbs, corms and trailing 

 stems of many varieties of herbs. Here, too, should be in- 

 cluded certain buds, such as the separable buds of pondweeds 

 and bladderworts; and the ofl'sets, stolons, suckers, runners, 

 and other branches with propagative tendencies. The leaf of 

 the walking-fern, and the leaves of some begonias have strong 

 propagative power. In mosses almost any portion of the body, 

 if isolated, proceeds to develop a new individual. 



Reproduction. Reproduction in the narrower sense, as it 

 takes place in organisms that have developed the cell habit, 

 begins by the formation upon the parent body of special re- 

 productive cells. These are either perfect or imperfect. Per- 

 fect reproductive cells are those that, after separation from the 

 parent body will, if conditions are favorable, develop into new 

 organisms. Such cells are called spores. Imperfect reproduc- 

 tive cells are those that will not normally at once develop into 

 new organisms, but will fuse together in pairs as a preliminary 

 to development. Such fusing cells are called gametes, and ordi- 

 narily a division of labor exists among gametes in view of which 

 some, in a species, are motile, or at least mobile, and active, 

 while the others are quiescent or passive. The motile gamete 

 is called a spermalozoid and the (|uiet gamete is called an egg. 

 In certain lower algae, such as the water silk, both gametes are 

 provided with swimming lashes and are conscfiuently motile. 

 In higher types, however, one gamete retained the motile char- 

 acter while the other lost it and as a consequence of its quiet 

 life, grew larger. Thus arose the distinction between male 

 and female cells, a distinction thai lies almost as deep as that 

 between plant and animal cells. In b(Hh kingdoms similar 

 conditions have arisen, and in both, the formation of eggs and 

 sperms is a normal and constant character in all species above 

 the very lowest in the scale. In both kingdoms the sperms 



