PHAMBMOGAMIA. 391 



otherwise different from foliage leaves, and containing little 

 or no chlorophyll ; they are usually of some other color than 

 green, from the presence of soluble coloring-matters in their 

 cells. These modified 2iarts, together with the organs more 

 immediately connected with the male and female reproduc- 

 tive cells, constitute what is known as the flower. 



499. — The ovule, in its development, becomes surrounded 

 by one or two thin cellular coats, which grow from its base, 

 and almost completely enclose it, a little orifice only, the 

 micropyle, being left at its apex. In the lower Phanero- 

 gamia (the Gymnosperms) the ovule enclosed in its single 

 (rarely double) coat is otherwise naked, while in the higher 

 classes — viz., the Monocotyledons and Dicotyledons — it is en- 

 closed within the cavity of the ovary, a phyllome structure, 

 or, as it is commonly described, a modified leaf, which is 

 folded involutely so as to form a cavity. 



500. — In the fertilization of the germ-cell there are no 

 spermatozoids developed ; instead of jiroducing these, the 

 pollen grain develops a long slender tube, the pollen tube, 

 which penetrates the tissue of the ovule, and comes in con- 

 tact with the germ-cell in the embryo sac. The result of 

 fertilization is always the formation of a suspensor (some- 

 times called the pro-embryo) essentially like that in the 

 Selaginellm and Isoetem, and, at the lower end of this, an 

 embryo, consisting of a short stem, bearing generally one or 

 more rudimentary leaves {cotyledons) at one extremity, and 

 a rudimentary root at the other. The embryo grows at the 

 expense of the endosperm, upon which it gradually en- 

 croaches, and in many orders entirely displaces. While the 

 embryo is form.ing, the ovule becomes greatly enlarged, and 

 its outer coat generally much thickened and hardened ; it is 

 now called the seed, and soon separates at its base from the 

 parent plant. 



501. — After a longer or shorter period of rest the seed 

 germinates, the root and stem elongate, and the former 

 pushes out through the micropyle ; in those seeds in which 

 much of the endosperm remains,* or in which the cotyle- 



* Seeds wliich contain endosperm are, in tke ordinary' descriptive 



