342 



BOTANY 



E 



is usually preceded by a repeated division of the nucleus (Fig. 306). The em- 

 bryo is always provided with an elongated suspensor, and usually grows from a 

 single apical cell (Fig. 306, C), which is later replaced by a group of initial cells. 

 The cotyledons range from two to six or more. 



The ripe seed is provided with a hard integument, or Testa, within 

 which lies the embryo surrounded by the endosperm, or prothallial 

 tissue (Fig. 286, B). In Cephalotaxus (Fig. 308, F) the outer part 



of the integument be- 

 comes pulpy, as it does 

 in Cycas, and in Taxus 

 a special outer fleshy 

 integument, or Aril, is 

 formed. The scales of 

 the cone usually become 

 hard and woody, but in 

 some Cupressinese e.g. 

 Juniperus they become 

 pulpy and coherent, so 

 that the cone resembles 

 a berry. 



G 



Germination (Fig. 307) 



FIG. 307. Pinus Virginiana, germination of the 

 seed. (A, B, X 4; C, X 3; D, X 2.) E, median 

 section of D, more enlarged. F, cross-section 

 of the stem of the seedling, showing the ring of 

 vascular bundles. G, similar section of the root ; 

 both enlarged. 



The germinating seed 

 absorbs water, and the 

 embryo begins to enlarge, 

 drawing upon the endo- 

 sperm, whose cells are 

 filled with reserve food, 

 especially oil and albu- 

 minous granules. Chloro- 

 phyll may be developed while the cotyledons are still enclosed in 

 the seed. 



The root, which is directed toward the opening in the integument 

 (Micropyle), pushes out through it, and bends down into the earth. 

 As the cotyledons exhaust the contents of the endosperm-cells they 

 withdraw from the seed-coat, which is cast off. A section through 

 the apex of the young seedling shows the conical apex of the stem 

 surrounded by the cotyledons. Each of the latter is traversed by a 

 single vascular bundle, which bends down into the stem. This in 

 section shows the circle of separate collateral bundles, which are the 

 primary leaf-traces. These soon become connected by a ring of cam- 

 bium, developed between xylem and phloem, and also between the 

 bundles, and the secondary thickening of the stem begins. 



