20.2 VEGETABLE ORGANOGRAPHY. 



in the roots being in general devoid of true hairs, to 

 which, in order to designate their situation, I have given 

 the name of Radical Hairs. — (Book i. ch. 10, sect. 7.) 



The radicle of the embryo, whatever be its form, is 

 perceived — 1st, in the seed before germination, because 

 it is always directed outwards — a very important charac- 

 ter to observe in Monocotyledonous plants, where it is 

 sometimes the only one by which we can readily dis- 

 tinguish the two extremities of the embryo ; 2d, after 

 germination ; because, with a very small number of 

 exceptions, as the Misletoe, the radicle is directed 

 towards the centre of the earth. This direction is so 

 decided that it presents itself under the most different 

 circumstances. We observe in particular, that whatever 

 be the position of the germinating seeds, the radicle is 

 always directed downwards, and if one more or less 

 developed be turned to the zenith, it always tends to 

 return of itself, so as to resume its natural position. 

 The cause of this phenomenon is an object of delicate 

 physiology, which will be discussed elsewhere ; I only 

 mention the fact here, as a distinctive character of ger- 

 minating radicles. 



The Plumule (plumula) is, as we have said, the stem 

 of the embryo or young plant, already present in the 

 seed or at germination ; it is distinguished, whatever be 

 its form, by characters opposite to the preceding, viz. 

 because in the seed it is directed inwards ; at germina- 

 tion, because it has a tendency to rise towards the 

 zenith, becoming green when exposed to the light, and 

 presenting all the other characters of stems. It ma}* 

 be divided into two parts, which Richard has called the 

 cauliculus and the gemmule. 



The Cauliculus is that part of the plumule which is 

 between the neck and the cotyledons ; the Gemmule 

 (gemmula) that which is above the cotyledons; in 



