G YM NO SPERM A E. CONIFER A E. 



3^9 



glauca and Eiicephalartos. According to Reinke and Strasburger, only the secondary 

 roots which come up to the surface of the ground branch dichotomously. By the 

 elongation of the cotyledons which remain in the endosperm and absorb the food 

 stored in it, their basal portions and the primary bud, iht plumule, which lies between 

 them are thrust out of the seed. Bo;h the portion of the axis which bears the 

 cotyledons and that which developes immediately above it continue very short, 

 while a considerable increase in circumference is produced immediately below the 

 apex by extensive development of parenchymatous tissue ; thus the stem assumes 

 the shape of a roundish tuber which it also maintains in many species. 



B. CONIFERAE'. 



Germmaimi. The endosperm surrounds the embryo in the form of a thick- 

 walled sac open at the root-end ; the embryo is straight in the central cavity of the 

 endosperm ; its axis is continuous behind with the rudiment of the primary root, and 

 bears at its anterior extremity a whorl of two or more cotyledons, between which it 

 terminates in a roundish apex (Fig. 250 /) ; the Taxineae, most of the Cupressineae 

 and Araucarieae have two opposite cotyledons ; but whorls of three or nine also 

 occur in the Cupressineae, and whorls of four in the Araucarieae, while the Abietineae 

 seldom have only two cotyledons, more commonly four, or even as many as 

 fifteen. 



When a seed lies in damp ground the endosperm swells and bursts the seed-coat 

 at the root-end of the embryo, which is thrust forth by the elongation of the axis and 

 developes a strong descending tap-root ; lateral roots then grow rapidly in acropetal 

 succession one after another from the primary root and afterwards branch, and in this 

 way the foundation is laid for the usually strong and persistent system of roots in the 

 Coniferae. When the root has issued from the seed the cotyledons also elongate 

 and push out their basal portions and the extremity of the axis that lies between 

 them, but remain themselves in the endosperm till this is exhausted; in Araiicaria 

 (sub-genus Colymhed) and in Gingko the hypocotyledonary portion of the axis continues 

 short and the cotyledons remain in the seed, but in most of the Coniferae it ultimately 

 becomes much elongated, turns sharply upwards, and breaking through the surface of 

 the soil draws the cotyledons with it; as soon as these have reached the light, the 

 hypocotyledonary portion of the axis straightens itself, the whorl of cotyledons 

 expands, and its leaves which have already become green beneath the ground perform 

 the part of the first foliage-leaves of the young plant, which has in the meantime 

 formed a bud with fresh leaves at the apex of its axis (Fig. 250). 



Growth and external differentiation. The terminal bud of the young stem grows 

 more vigorously than any one of the lateral shoots of later formation, and thus pro- 

 duces the primary stem as the direct prolongation of the axis of the embryo ; the stem 



' On the formation of the flowers see Rob. Brown, Misc. Bot. Works (,Ray Soc), i. p. 567. — 

 H. V. Mohl, Verm. Schr., p. 55.— Eichler, Ueber d. weiblichen BUithen d. Coniferen .Monatsber. 

 d. K. Ak. d. Wiss. Nov. 1881).— Hofmeister, Vergl. Untersuch. 185 1.— Strasburger, Die Conif. u. 

 d. Gnetac. Jena, 1872 ; — Id. Die Angiosp. u. d. Gymnosp. Jena, 1879.— [Goroschankin, Zur Kenntn. 

 d. Corpuscula b. d. Gymnosp. (Bot. Ztg. 1885).] Strasburger's works quoted above contain also 

 a very complete account of the literature of the subject. 



