ORGANS OF REPRODUCTION. 



>37 



Fig. 748. 



little rounded or somewhat oval cellular body at the end of the 

 suspensor {fig. 746, 1). This cellular body continuing its growth 

 soon begins to alter in shape, and assume that of the embryo, of 

 which it is the early stage ; thus, the upper extremity in contact 

 with the suspensor, tapers somewhat and forms the radicle, while 

 the lower extremity gradually becomes divided into lobes, which, 

 by increasing in growth, form the cotyledons : the suspensor, 

 during this gradual enlargement, dies away, and the development 

 of the embryo is completed. The different stages in the develop- 

 ment of the embryo are well illustrated in fig. 746, 1, 2, 3, 4. 

 From the axil of the cotyledons, the plumule is subsequently 

 developed. The formation of the monocotyledonous embryo is 

 essentially the same, except that the lower 

 end remains undivided. From this mode 

 of development of the parts of the embryo, 

 it must necessarily follow, that the radicle 

 is pointed towards the apex of the nucleus 

 or micropyh {figs. 737 and 761), and the 

 cotyledonary portion towards the opposite 

 extremity or chalaza. 



There are some natural orders which 

 offer an exception to the above process of 

 development. Thus in the Orchidacefe, 

 Orobanchaceae, and Balanophoraceae, the 

 radicle and cotyledons are never clearly 

 distinct from each other, but the embryo 

 appears to be arrested at one of the early 

 stages of its development. 



It sometimes happens that more than Fig 

 one embryo is developed in a seed. This 

 is very commonly the case in the Orange, 

 the Mistletoe, and as a constant character 

 in Gymnospermous Plants (see EEPRODrc- 

 TiON OF Gtyxnospermia). Of these em- 

 bryos, only one usually becomes perfectly 

 developed. Plants thus producing more 

 than one embryo are said to be 'polyerahryonic. With these 

 remarks upon the development of the embryo generally, we 

 now proceed to the description of that of Monocotyledonous 

 and Dicotyledonous Plants. 



a. Tlie Monocotyledonous Embryo. — The parts of the mono- 

 cotyledonous embryo are, in general, by no means so apparent as 

 those of the dicotyledonous. Thus the embryo at first sight 

 externally, usually appears to be a solid undivided body of a 

 cylindrical or somewhat club-shaped form, as in Triglockin {fig. 

 748); if this be more carefully examined, however, a little slit, 

 /, or chink, will be observed on one side near the base ; and if a 

 vertical section be made parallel to this slit, a small conical pro- 

 z 



Vertical section 

 of a carpel of a species 

 of Triglochin. p. Peri- 

 carp, s. Stigma. 3. Seed. 

 r. Rapbe. /. Funiculus. 



c. Chalaza. Fig. 748. 



Embryo of Triglochin. 

 r. Radicle. /. Slit cor- 

 responding to the plu- 

 mule, c. Cotyledon. From 

 Jussieu. 



