Minnesota Plant Life. 



i8i 



club-moss, these seed-plant spores are not ejected from their 

 spore-cases, while, just as in the smaller club-moss, they de- 

 velop females which are retained within the spore-wall and upon 

 the bodies of these females egg-cells are formed. How is it 

 possible for such an egg, developed and retained within the 

 tissues of a spore-case, to ob- 

 tain fecundation? Here comes 

 into play an adaptation on the 

 part of the male-plants of the 

 seed - producing varieties. 

 Where is one to look for the 

 male cottonwood tree? Like 

 other male plants it originates 

 from a spore, not, however, 

 the large-spore, enclosed in the 

 rudimentary seed, but the 

 small-spore known as the pol- 

 len-grain, developed in large 

 numbers upon special leaves 

 known as stamens. What sort 

 of a plant arises when a pollen 

 spore germinates? Before re- 

 plying to this question another 

 must be asked. Where does a 

 pollen-spore germinate? Not 

 upon the soil, or in the water, 

 as did the small-spores of ferns 

 and smaller club-mosses, but 

 upon a certain portion of the 

 body of a spore-producing 

 plant of its own species, a part 

 usually in close proximity to 

 the rudimentary seeds. This 

 area upon which a spore of the smaller kind is able to germinate 

 is known as the stigma in higher flowering plants, but in the 

 lower families the pollen-spores fall immediately upon the im- 

 mature seeds. 



Breeding habits of seed-plants. Returning now to the ques- 

 tion, what sort of a plant arises when a pollen-spore germinates, 



Fig. 69. Diagram of an ovary, with one seed- 

 rudiment, in a higher .seed-plant, s. The 

 ,?//^;«a, where two pollen-spores have germi- 

 nated; o, wall of ovary; f, stalk of ovule; 

 ai and ii, rudimentary seed-coats; n, spore- 

 case, with single large spore, which has 

 germinated to produce the reduced female 

 plant; k, the egg; e, the body which forms 

 the albumen; b, other cells of the female. 

 The male plant is shown as a tubular 

 thread growing towards the egg. After 

 Atkinson. 



