514 Minnesota Plant Life. 



which the spores form a superficial layer, and the various cap- 

 sules containing numerous mother-cells — such as those of 

 mosses and ferns, or the pollen-sacs of flowering plants. An- 

 other aggregate body is seen in the fruit of the cup-fungus, 

 where the lining consists of numerous sacs in each of which a 

 definite number of spores is formed. 



In any case, spores arise by the division of preexisting cells 

 of the body and, after formation, they are either distributed 

 to a distance or retained upon the body and permitted to ger- 

 minate near the point where they arose. The first is the primi- 

 tive and ordinary treatment of spores, but certain special types, 

 such as the large-spores (embryo-sacs) of seed-producing plants, 

 are retained in the rudimentary seeds where they were formed 

 and go through their germination processes w^ithout distribu- 

 tion to a distance. While maturing, spores are protected, 

 moistened and nourished by various devices. 



Distribution of spores. If spores are to be removed from 

 the body of the plant producing them, some method of sepa- 

 rating them from their point of origin must be devised, and 

 some agency must be found that will transport them to a spot 

 where they may be able to germinate. Of abstricted spores, 

 such as those of mushrooms, the separation is little different, in 

 most instances, from a mere falling ofif the support. Yet in 

 certain cluster-cup fungi special wedges of cell-wall-substance 

 are produced between the successive spores of a chain and by 

 means of these they are loosened from each other. And in the 

 fly-cholera fungus the terminal spore is projected from its stalk 

 by an explosive mechanism that not only separates the spore 

 from the body of its parent, but throws it some little distance 

 from its point of origin. 



In order that spores formed internally, within spore-mother- 

 cells, may be distributed, the walls of the spore-mother-cells 

 must be broken or dissolved. Sometimes only the ends of the 

 sacs break down to release the spores, as in cup-fungi and disc- 

 fungi, and in such the release is sometimes of an explosive 

 character. Again the whole wall of the spore-motlicr-ccll may 

 dissolve. This is true of mosses and ferns, of club-mosses and 

 higher plants. Jn these instances the spores come to lie freely, 

 in the form of a dry powder, within the capsules where the 

 spore-mother-cclls were developed. 



