210 



ORGANOGRAPHY. 



BOOK I. 



germination, emitting the radicle, and has been named by 

 Gtertner the emhnjotega. 



'At the apex of the seed in the orange, and many other 

 plants, may be perceived upon the testa a small brown spot, 

 formed by the union of certain vessels proceeding from the 

 hilum : this spot is the chalaza (Plate VI. fig. 11. b). In the 

 orange it is beautifully composed of dense bundles of spiral 

 vessels and spiral ducts, without woody fibre. The vessels 

 which connect the chalaza with the hilum constitute a parti- 

 cular line of communication, called the raphe : in most plants 

 it consists of a single line passing up the face of the seed ; but 

 in many Aurantiacese and Guttiferae it ramifies elegantly ni 

 every direction upon the surface of the testa. 



The raphe is always a true indication of the face of the seed; 

 and it is very remarkable that the apparent exceptions to tliis 

 rule only serve to confirm it. Thus, in some species of Euony- 

 mus, in which the raphe appears to pass along the back, an 

 examination of other species shows that the ovules of such 

 species are in fact resupinate ; so that with them the hne of 

 vascularity representing the raphe is turned away from its true 

 direction by peculiar circumstances. In reality, the chalaza is 

 the place where the secundine and the primine are connected ; 

 so that in orthotropous seeds, or such as have the apex of the 

 nucleus at the apex of the seed, and in which, consequently, 

 the union of the primine and secundine takes place at the 

 hilum, there can be no apparent chalaza, and consequently no 

 raphe : the two latter can only .exist as distinct parts in 

 anatropous seeds, when the base of the nucleus corresponds to 

 the geometrical apex of the seed. Hence, also, there can never 

 be a chalaza without a raphe, nor a raphe without a chalaza. 



Something has already been said 

 about the aril {Jig. 187. and 188.) 

 when speaking of the ovule; but 

 it more properly comes under con- 

 sideration along with the ripe seed. 

 As a general rule it may be stated, 

 that every thing proceeding from 

 the placenta and not forming part 

 of the seed is referrible to the 

 aril. Even in plants like Hib- 



188 



Am I if 



