Aquatic Seed Plants 151 



closely overlapping two-lobed leaves, and emits a few 

 rootlets from the under side which hang free in the 

 water. In the back waters about the Illinois Station at 

 Havana, Illinois, AzoUa forms floating masses often 

 several feet in diameter, of bright red rosettes. 



Shoreward there are numerous pteridophytes grow- 

 ing as rooted and emergent aquatics; the almost grass- 

 like Isoetes, and the marsh horsetails and ferns, but 

 these latter differ little from their near relatives that 

 live on land. 



Aquatic Seed Plants — These are manifestly land 

 plants in origin. They have much stiffening in their 

 stems. They have a highly developed epidermal 

 system, often retaining stomates, although these can 

 be no longer of service for intake of air. They effect 

 fertilization by means of sperm nuclei and pollen tubes, 

 and not by free swimming sperm cells. 



Seed plants crowd the shore hne, but they rapidly 

 diminish in numbers in deepening water. They grow 

 thickest by the waterside because of the abundance of 

 air moisture and light there available. But too much 

 moisture excludes the air and fewer of them are able to 

 grow where the soil is always saturated. Still fewer 

 grow in standing water and only a very few can grow 

 wholly submerged. Moreover, it is only in protected 

 shoals that aquatic seed plants flourish. They cannot 

 withstand the beating of the waves on exposed shores. 

 Their bodies are too highly organized, with too great 

 differentiation of parts. Hence the vast expanses of 

 open waters are left in possession of the more simply 

 organized algae. 



An examination of any local ffora, such as that of 

 the Cayuga Lake Basin* will reveal at once how small a 

 part of the population is adapted for living in water. 



*Tlie following data are largelj- drawn from Dudley's Cayuga Flora, 1886. 



