190 VEGETABLE ORGANOGRAPHY. 



leaves, owes its existence to its being more exposed to 

 the air than the other parts of the spermoderm : what 

 confirms this opinion is, that sometimes the testa cannot 

 be distinguished, or at least, is not of its usual texture 

 in all seeds which are invested with an epidermis, and 

 especially in those which are united to the pericarp. 



The endopleura, or inner coat of the spermoderm, is 

 exactly in the seed what the endocarp is in the fruit, 

 that is to say, the upper face of the leaf folded upon 

 itself; this membrane never has either the shining ap- 

 pearance or solidity of the testa ; it is almost always of 

 an uniform white colour, and composed of a cellular 

 tissue, which, one would think, ought readily to absorb 

 water; but the case is quite the contrary, for it contains 

 the aqueous juices of the young seeds without absorbing 

 them, and at the period of germination it prevents the 

 water from passing directly to the embryo. The endo- 

 pleura seems moulded upon the Nucleus <of the seed 

 (this name is given to the whole of what is contained 

 within the spermoderm); but, in reality, it is the nucleus 

 that is originally moulded, as it were, in the empty 

 space within the spermoderm, which, when it begins to 

 grow, it distends. 



The endopleura, at a certain point which is called 

 the Chalaza, gives passage to the vessels which bear 

 the nourishing or fecundating juices to the embryo. 



The mesosperm is in the seed, what the mesocarp is in 

 the fruit ; that is to say, the plexus of fibrous vessels 

 and of cellular tissue which is found between the two 

 membranes ; in fact, it is most frequently a very delicate 

 and scarcely apparent fibrous plexus ; it takes a fleshy 

 or pulpy consistence in but a very small number of 

 cases, as, for example, in Magnolia, Irisfcetidissima, &c. 

 The seeds which have this peculiarity, are named 

 Semina saccata in descriptive works ; the dry and 



