102 ' SEED. 



coats jf the seed are not always the same as tho-e that 

 covered the ovale. The outer covering is called by De 

 Candolle, the testa, the second the sarcodermis the inner the 

 endopleura. Much might be said of the origin of these integu- 

 ments, and the changes they unde.go in development, but it 

 would be of little interest to the student commencing' the sub- 

 ject. The testa presents a great variet}' of appearances in 

 different plants. 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 it 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, 



117. 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 

 is always the base of the seed 



118. The terms raphe and chaJaza have the same application 

 in the seed as in the ovule. In orthotropous and campulitropous 

 seeds, these parts are not oi)servable, 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 the necessity of its development is superseded by the contact 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, being an elevated ridge on one side, 

 and in the orange the situation of the chalaza is distinctly 

 marked by a small dark colored spot. The raphe does not al- 

 ways consist of a single bundle of vessels, but ramifies on the 

 surface of the seed, as may be seen by the veins on the surface 

 of the Almond, which are raiiiifications of the raphe. 



119. The embryo is the product of the action of the pollen. 

 If the ovule be dissected soon after impregnation, there will 

 be found within the nucleus and contiguous to the foramen a 

 minute speck, opaque and yellowis'i, which enlarges by the 

 absorption of the surrounding fluid ; this fluid is the amnios. 

 The minute speck becomes in its enlargement a distinctly or- 

 ganized body, and assumes in time the form of an embryo 

 plant. The embryo consists of three parts, the radicle, plu- 

 mula, and cotyledoriy some add a fourth a caidiculus or neck. 

 The radicle becomes by development the root or descending 

 axis of the plant, and the plumula the ascending axis or stem. 

 The cotyledons are to be the earliest leaves of the plant. 

 The cauliculus or neck is the imaginary point of separation of 

 the plumula from the radicle. Fig. 142, represents an embryo 



