516 Minnesota Plant Life. 



It makes a difference, in the economy of the plant, whither 

 the spores are carried, in the distribution. The chances against 

 their finding spots favorable for germination are met either by 

 their production in enormous numbers, or by highly accurate 

 methods of distribution. Pines illustrate the former condition, 

 while orchids, in the management of their pollen spores, illus- 

 trate the latter. Much depends upon the needs of the sporeling 

 the plantlet that arises from the spore, upon its germination 

 and many structures and habits of spores are determined by the 

 special requirements of the new plant. Thus, it happens among 

 scouring-rushes that certain spores will produce little male 

 plants, while others will produce small females. It is important 

 that these plants should not arise isolated from each other, for 

 then it would be difficult for them to breed. Therefore, scour- 

 ing-rush spores are provided with curious grappling append- 

 ages by which they cling together in groups. Again, in some 

 ferns, many club-mosses and all flowering plants two kinds of 

 spores are formed, differing in size. The large ones, contain- 

 ing more food material, are better suited to give birth to female 

 plants of the species, while the small ones, not so well nourished, 

 can produce only males. Females need generally to be larger 

 than males, for they have to form and nourish the larger gamete- 

 cells, the eggs. Such a difference in size of spores occasions 

 difference in their distribution and since it is more economical 

 to transport the smaller bodies it happens that in higher plants 

 the large spores are not distributed at all, and the small ones 

 are brought near them so that upon germination of both, the 

 male and female plants will not be too far apart. Various de-- 

 vices are employed in the different families. Very remarkable 

 is the' behavior of the little water-fern, Azolla, in which a cluster 

 of small spores, embedded in mucilage and furnished with 

 barbed grappling appendages upon the group, is ejected from 

 the spore-case and is carried by water currents to find an 

 anchorage among slender, thread-like appendages of the large 

 spore, provided for that purpose. Under such an adaptation 

 the two sexes arise in close proximity. 



In flowers all the extraordinary arrangements for distribu- 

 tion of pollen are associated with the peculiar habits of the males 

 and females of the higher plants. The female originates, as a 



