104 SEED. 



the two great classes of flowering plants, on the fact that the 

 radicles of one were enclosed within a sheath, while the radi- 

 cles of the others were destitute of such a covering. 



121. From the above description there are of course some 

 exceptions, but all of which may be reduced to the common 

 type. A slight variation is common, in which 

 Ifib^jlllll the plumula is distinguishable from the other 

 ^parts and lies within a minute cleft near the 

 base of the embryo, from which it issues on the 

 commencement of germination. Fig. 144, repre- 

 sents an embryo of one of the grasses ; a the co- 

 HL^ tyledon, h the radicle and c the fissure, in which 

 the plumula lies. 

 3 122. The embryo instead of being surrounded by 

 the albumen, often lies on one side near the base 

 and in direct contact with the testa. On the side next the 

 testa, a slit is observed like the one above described, and if 

 this embryo be divided vertically there will be discovered with- 

 in small rudimentary leaves proving this to be the plumula. 

 That part of the embryo lying between this and the albumen, 

 is the cotyledon and a little below this, and on the opposite side 

 in some species, as the wheat, is another similar body which is 

 much smaller, but it is generally admitted to be of the same na- 

 ture, thus proving that plants strictly conforming in every other 

 respects to those called monocotyledons, have two cotyledons ; 

 but in all such cases the cotyledons are alternate and never 

 opposite. The embryo of the Pine, although reckoned among 

 the dicotyledons, has several cotyledons ; but these are oppo- 

 site forming a whorl. The distinction made by this arrange- 

 ment of the cotyledons, being alternate in Endogens, and op- 

 posite or verticillate in Exogens, will always be a guide in de- 

 termining to which an individual should belong. An equally 

 sure mark of distinction is the mode of germination whether 

 of the endorhizal or exorhizal manner. 



123. The albumen when present is a substance surrounding 

 the embryo, and is supposed by some to be the solidified am- 

 nios. It varies remarkably in consistence and appearance, 

 sometimes soft and fleshy, at others hard and bony. In size 

 it varies from an exceedingly small quantity as in the grasses, to 

 the amount of several ounces in the cocoanut. It is some- 

 times perforated by dry cellular tissue, in which state it is 

 said to be ruminated. 



To determine the several parts of the seed which we have 

 above defined, and the position they occupy in reference to 

 each other is of great practical importance in descriptive 



