554 LIFE-HISTORIES 



(or embryo-sac) has been developing some very simple archegonia 

 (a), consisting only of a large egg-cell (o), and one or more very 

 small cells (c) representing the neck. See also Fig. 379, A . Presently 

 the tip of a pollen-tube bearing the male nucleus reaches the egg- 

 cell and discharges its nucleus into the female protoplast (Fig. 379 B). 

 The male and the female nucleus fuse into one {€') and move to 

 the opposite end of the egg-cell, there to form a group of small cells 

 from which one or more embryos arise, but only one develops, in 

 each seed. As in Selaginella, certain cells form a suspensor which 

 pushes the developing embryo into the storage tissue of the game- 

 tophyte. But in the pine and spruce this vegetative part of the 

 nurse-plant, because of its long connection with the parent, is able 

 to draw into itself a continued supplj^ of nutritive material. Part 

 of this nourishes the embryo till it develops root, stem, and leaves, 

 while a surplus is stored around it as seed-food for the use of the 

 plantlet when it has left the parent, and is readj' to germinate 

 (Figs. 379, 380). Not only is abundant food thus supplied to and 

 for the embryo, but the sporangium wair(nucellus and integument) 

 and the sac-leaf (cone-scale or carpel) are so well nourished after 

 fertilization has taken place, that they grow enormously and be- 

 come much hardened as organs of protection. The ripened ovule 

 thus becomes a seed, and finally, as already described, separates 

 from the parent and is aided in its aerial voyage to a home for life, 

 by a wing derived from the carpel. The young sporophyte has 

 simply to grow after the manner of its kind to become a tree and 

 produce gametophytes which shall cooperate in the formation of 

 highly favored offspring. 



In view of the many resemblances between Pinacese and 

 Lycopodiacege it has been thought that plants closely related 

 to the club-moss trees of tlie coal-period may have been the 

 ancestors of both of these cone bearing groups. It should 

 be said, however, that the remains of extinct gymnosperms 

 represented by Cordaites (Fig. 277, 5) contemporaneous with 

 Lepidodendron, show resemblances to the ancient ferns 

 which indicate that the ancestor of the conifers was more 

 fern-like than might appear merely from a comparison of 

 modern types. 



Cycas (Fig. 381) shows even closer affinity with ferns, as for in- 

 stance, in the ample branched foliage-leaves which unroll as they 

 develop, and the numerous sporangia borne upon a sac-leaf. In 

 general the life-history is similar to that of Pinus, pollen spores 

 being carried by the wind to a little chamber at the tip of a naked 

 ovule to fertilize an egg-cell; but in this case the microspore upon 

 germinating ]5roduoes in the pollen-tube two motile gametes pro- 



