SEED. 93 



The face of a seed is that part of it parallel with the placenta ; 

 or when the raphe is present, this organ, with only few ex- 

 ceptions, runs over the face. The opposite surface is the back. 



159. The parts of the seed demanding our attention are the 

 covering, hilum, raphe, chalaza, embryo, and albumen. 



The integuments or coverings of the seed are subjects of much 

 discussion, both as to their number and constitution. The di- 

 versity of opinion on the subject, originates, no doubt, in a great 

 measure, from the change they undergo, from the transforma- 

 tion of the ovule into a seed. One would naturally suppose 

 that the integuments of the seed would be the same as those of 

 the ovules. But this is not the case in many instances. Three 

 have been named by different writers, corresponding to the three 

 layers of the ovule ; but the coats of the seed are not always the 

 same as those that covered the ovule. The outer covering is 

 called by De Candolle the testa, the second the sarcodermis, the 

 inner the endopleura. The testa consists of cellular tissue, and 

 presents a great variety of appearances of form and color in 

 different plants. In some the cells are spiral without any mem- 

 brane ; and when moistened, uncoil in a beautiful manner, as in 

 those of the Salvia. In some cases it is smooth and polished, 

 in others rough and irregular, marked by dots and projecting 

 points ; in some it is covered with hair, as in the cotton and 

 epilobium, which is called coma; in others it is furnished with 

 wings, as in the Gladiolus and Bignonia. In some it is ribbed, 

 in others it is pitted and marked by irregular depressed lines. 



160. The hilum is the point by which the seed is attached to 

 the placenta ; it is frequently distinguishable by being of a dif- 

 ferent color, and having the appearance of a scar. The hilum 

 always marks the base of the seed, as the micropyle (mikros, 

 small, and pule, gate) does its apex, toward which the root of 

 the embryo is directed. 



161. The terms raphe and chalaza have the same application 

 in the seed as in the ovule. In orthotropous and campylotro- 

 pous seeds these parts are not observable, since the chalaza is co- 

 incident with the hilum ; and as the raphe is the bundle of ves- 

 sels conveying nourishment from the hilum to the chalaza, the 

 necessity of its development is superseded by the contact of these 

 parts. The raphe is easily observed on the seeds of the Apple 

 and Orange, running between the outer and inner integuments, 

 being an elevated ridge on one side; and in the orange the situa- 



Which is the face of the seed?— 159. What did De Candolle call the dif- 

 ferent coverings of the seed ? Of what does the testa consist ? What of 

 its different appearances?— 160. What is the hilum ? How is the position 

 of the embryo known?— 161. When is the raphe euCv observed? 



