Minnesota Plant Life. 



195 



wall. In higher seed-plants there is no definite egg-organ, but 

 the egg lies loosely among the other cells of the extremely re- 

 duced and degenerate female. 



Relation between lower seed-plants and primitive seedless 

 plants. A very remarkable character, which shows clearly the 

 connection between smaller club-mosses and lower seed-plants, 

 is not known to be presented by either of the Minnesota fam- 

 ilies of the latter group, though it is now described for two that 

 are exotic. It is, however, a fact of such extreme interest that 

 it should be mentioned at this point. 



Fig. 7.5. Rock on the St. Croix river, near Taylor'.s Fall.s. Show.s zonal distribution of trees. 

 White pine.s stand on top of the rock, and birches and poplars on the sides. After photo- 

 graph by Mr. H. C. Cutler. 



In the sago-palms and ginkgo trees the pollen-spores fall as 

 in other naked-seeded plants, upon the ends of the immature 

 seeds, then germinate and produce their pollen-tubes. In the 

 end of each pollen-tube in these plants there develop a pair of 

 motile spermatozoids provided with swimming lashes. In the 

 cycad family to v.'hich the sago-palm belongs, are a few Amer- 

 ican species finding their home in Florida. In these when 

 the pollen-tube comes close to the egg a motile spermatozoid 

 swims into it, peeling ofif its swimming-lashes in a spiral coil 



