FRUIT. 85 



much exceeding in any case the cells of which the nucleus is 



composed. (Fig. 139.) This is called the embryo 



sac, and it is in this that the embryo appears rig. 139. 



after the perfection of the flower. The embryo is 



always found at the apex of the nucleus, and of 



course immediately within the foramen, through 



which the pollen tubes enter. It is suspended in 



the embryo sac by a thread called a suspensor. 



The radicle, or root part of the embryo, is always 



toward the foramen, and the plumula toward the 



chalaza or hilum. Embryos of orthotropous seeds 



are, of course, inverted. 



142. The contents of the ovule are variously changed after 

 impregnation. Sometimes the embryo consumes the whole 

 contents of the nucleus, when the seed is said to have no albu- 

 men ; at other times the embryo remains very small, and the 

 nucleus becomes filled with starch, or oils, or other materials 

 of various consistence and forms, which is called albumen. 



143. When the ovule rises from the base of the ovary, it is 

 called erect; when from a little above the base, ascending; when 

 it hangs from the summit of the cavity it is pendulous ; and 

 when from a little below the summit, it is suspended. 



Fruit. 



144* The fruit is defined, in botany, to be the pistil or ovary 

 arrived at maturity, including sometimes accessory parts. 

 This definition plainly gives greater extension to the term than 

 it has in common language, as it includes every kind of pro- 

 duct which has the mature ovary as a component. 



The normal form of fruit, and the type to which all varieties 

 should be reduced, would seem to be that in which the seeds 

 are contaiued in a pericarp, with the carpels leaf-like in their 

 constitution and appearance, as the Hibiscus, Bean, Cabbage, 

 <kc. In these cases it requires no great stretch of the imagina- 

 tion to conceive the ovary composed of leaves slightly modified ; 

 but from this type there are remarkable variations, caused by 

 one or more of the following causes. The suppression or hard- 

 ening of parts in some, their unusual development in others, 

 and the union of other organs with the ovary, are the prin- 

 cipal causes of variation. By carefully noticing these occa- 



141. What is the embryo sac? How is the embryo suspended? — 142. 

 When has the seed no albumen ? What takes place at other times ? — 143. 

 When is- the ovule erect ? When ascending? Pendulous? Suspendodf 

 —144. What is the fruit ? What is the normal form of fruit ? 



