Ch. XIII] THE SEED PLANTS 513 



phytes as forest plants, are competing with the Bryophytes 

 as carpet plants, are intruding among the Algae as water 

 plants, and are even entering the domain of the Fungi as 

 parasites. 



Reproduction in Spermatophytes occurs to some extent 

 through various minor vegetative methods, but the prin- 

 cipal form is sexual, which is universally present. The 

 method thereof has already been explained (pages 269-79). 

 The egg cell lies in an embryo sac which forms in a nucellus 

 inclosed by integuments except for a micropyle. This ovule 

 is commonly but not always inclosed in an ovary provided 

 with style and stigma, and surrounded by showy or protec- 

 tive parts. The sperm cell is formed in the pollen grain 

 which develops in the anther of the stamen, and is trans- 

 ferred to the vicinity of the ovule not by any power of 

 locomotion of its own but by action of wind, insects, etc. 

 From the pollen grain develops a haustorial tube which 

 grows through all intervening tissues to the egg cell, to which 

 it brings a sperm nucleus. The fertilized egg cell grows to an 

 embryo plant which is nourished from endosperm developed 

 within the embryo sac ; and this embryo, with its food and 

 the thickened ovular coats, separates from the ovary and 

 plant as the seed. This seed is the dissemination stage of 

 the plant, and as such is a resting body which can long en- 

 dure dryness and other unfavorable conditions ; and in this 

 state it is carried afar by winds, water currents, or various 

 animals according to the structural features it presents. 

 Later, under favorable conditions, it germinates, and pro- 

 duces a new plant, which develops new egg cells and sperm 

 cells in its turn. 



The homologies of the parts in Spermatophytes and 

 Pteridophytes are perfectly clear (Fig. 361). The familiar 

 conspicuous plant is in both the sporophyte. The spores, in 

 Spermatophytes as in Selaginella, are of two kinds. The 

 megaspores, which remain permanently attached to the par- 

 ent plant, are the embryo sacs, in the early stage with a 

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