SEED PLANTS 



165 



goniatse, and the egg thereupon begins to grow and 

 develops into the embryo-sporoph3'te, while the sur- 

 rounding cells of the gametophyte become filled with 

 food-materials and 

 are known as the 

 " endosperm." The 

 wall of the sporan- 

 gium now hardens, 

 while the outer tissues 

 of the integument, 

 become pulpy, so that 

 the ripened seed looks 

 very much like the 

 fleshy fruit of a plum 

 or cherry. 



That the Cycads 

 represent a very an- 

 cient type is shown 

 by their fossil re- 

 mains, which indicate 

 that during the Mes- 

 ozoic age they were 

 among the most abun- 

 dant plants. They 

 occurred in great num- 

 bers, and comprised 

 many more genera 

 and species, as well 

 as 



Fig. 41 (Coniferse). — A, a branch of a fe- 

 male plant of the common yew (Taxus) , 

 one of the simplest Conifers ; ma, young 

 female flower; /;■, ripe fruit; B, a single 

 female flower, consisting of an ovule, or 

 macrosporangium, ma, surrounded by a 

 number of scale-leaves ; C, a section of 

 the flower, showing the terminal spo- 

 rangium (ovule), in, surrounded by the 

 Integument, in, and the scales, .«c; D, 

 section of an older ovule, showing the 

 large macrospore (" embryo-sac "), up ; 

 E, the ripe fruit, with one side of the 

 cup-shaped aril, or, cut away to show 

 the seed, s; the seed is the matured 

 ovule, the aril a special structure which 

 grows up about the seed; F, a male 

 flower of Taxus, showing the umbrella- 

 shaped sporophylls, each bearing sev- 

 eral microsporangia upon the lower 

 surface ; G, a single sporoijhyll ; mi, 

 the sporangia; H, a leaf of Gingko, 

 showing the fern-like form and vena- 

 tion. (Figs. F, G, after Eichler.) 



individuals, than 

 at present. The first evidences of the existence of 

 Cycads occur in the Carboniferous rocks, but in small 

 numbers ; but in the Mesozoic rocks, as already stated, 



