1 82 Minnesota Plant Life. 



the reply is, a delicate thread, like a cobweb, comes into exist- 

 ence and grows much as a parasitic fungus filament would 

 grow through the tissues of the immature fruit down to the 

 surface of the large-spore, imbedded in the rudimentary seed. 

 By this time the female has developed within the large-spore and 

 has produced her egg. The end of the pollen-tube, as the male is 

 termed, penetrates the wall of the large-spore and transfers a 

 male nucleus, or sperm, which fuses with the egg and thus 

 fecundation is accomplished. Then the egg becomes an embryo 

 which grows and produces a short stem, one or more seed- 

 leaves (in most plants) and a root. While the embryo is devel- 

 oping, the tissues of the spore-case and the membranes sur- 

 rounding it become modified into the outer layers or seed-coats. 

 When the embryo pauses in its growth and passes into a tem- 

 porary dormant condition the seed is said to be ripe. It may 

 not, however, be able at once to germinate. 



If the reader has closely followed this explanation he will 

 be aware that is is improper to call a pollen-producing plant 

 a male and he will understand that there is no comparison at 

 all between the sowing of pollen-spores on a stigma where 

 they are to germinate and a breeding habit, although the older 

 botanists supposed that such analogy existed. It is found that 

 seed-producing plants, like the smaller club-mosses, have two 

 sorts of spores, small-spores producing males, and large-spores, 

 females. As in the lower type, so also in the seed-plant, there is 

 a retention of the female within the wall of the spore from which 

 she originated. Unlike the smaller club-mosses, the male plant 

 is not retained within the wall of the small-spore, but pro- 

 trudes in the form of a thread of miscroscopic minuteness. The 

 retention of the large-spore within its spore-case, together with 

 the adaptation of the male plant so that fecundation may take 

 place without the opening of either the large-spore or its case, 

 lays the foundation for that compound and complex body, the 

 seed. 



By these devices the embryo is kept in close proximity to 

 the vegetative areas of its species and in a pine seed there are 

 represented three successive generations. The coats of the seed 

 and sometimes a portion of the food-supply, as in water-lilies, 

 belong to the older spore-producing generation, for they are 



