Seeds and the Morphology of Seedlings. 5 



acter often occurring in the seeds of plants belonging to the Order 

 Euphorbiacese. 



Remove the outer-seed-coat being careful not to injure the parts 

 within. 



The inner-seed-coat is delicate and membranous. It is apt to 

 break if an attempt is made to remove it. 



Split the seed in two. 



Each half of the seed appears like a cotyledon. 



A close examination will show that there is a considerable part 

 of the seed between the margin of the cotyledon and the seed- 

 coats. A cross-section of the seed shows this still more plainly. 

 Closer observation will show that the embryo is completely sur- 

 rounded by an oily albumen. The lower tip of the hypocotyl, 

 the place where growth begins, comes nearer to the coats than 

 any other part of the embryo. Further knowledge of the struc- 

 ture of the seed may be gained by making vertical sections at 

 right angles to the plane in which the cotyledons lie. At the 

 lowest point, i. e. , nearest the caruncle, will be seen the minute 

 hypocotyl, the lower tip of which is always found close to the 

 micropyle in any seed. This affords a "land-mark " from which 

 the relations of the other parts may be determined. 



The inner face of the cotyledon .shows three veins arising from 

 the base ; the central one or mid-rib gives off lateral veins 

 throughout most of its length. It is not often that the cotyledon 

 shows its venation in the seed. 



In the seed of Ricinus, the plumule is not developed until after 

 the seed has germinated. 



This is an albuminous seed. The contrast between an albumin- 

 ous and an exalbuminous seed is well illustrated in the Castor 

 Oil Bean and the Common Bean. It should be clearly under- 

 stood that the words " albumen " and *' albuminous," as used in 

 Plant-morphology, do not refer to the chemical compcsition of 

 the substance in question, but designate a particular part of the 

 seed, the chemical composition of which varies in different seeds. 



The germination of the seed of Castor Oil Bean exhibits cer- 

 tain very interesting features. Germination begins as in all seeds 

 at the lower tip of the hypocotyl. This penetrates into the soil, 

 its roots absorb the needed moisture. The cotyledons remain 

 within the seed-coats absorbing the nourishment there stored in 



