.STRUCTURE.] THE EMBRYO. 59 



embedded in jelly, as Gleditschia triacanthos. The 

 walls are not to be distinguished but by dropping on 

 them sulphuric acid, by which means the jelly is dis- 

 solved out. The interior of the cells is filled with mucus 

 (Schleim), a term used to distinguish it from jelly and 

 starch. This mucus is composed of globules, which are 

 coloured brown yellow by tincture of iodine. In Ca- 

 thartocarpus fistula resinous globules were found, and 

 in Mimosa pudica, crystals in the same position. This 

 jelly or gelatine between the cells, seems to be identical 

 with Mohl's intercellular substance, and it may be con- 

 jectured to be the basis from which the cells of the 

 albumen themselves are formed. 



The embryo (or corculum) (Plate VI. fig. 1. b, &c.) is a 

 fleshy body occupying the interior of the seed, and consti- 

 tuting the rudiment of a future plant. In most plants one 

 embryo only is found in each seed. It nevertheless occurs, 

 not unfrequently, that more than one is developed within a 

 single testa, as occasionally in the Orange and Hazel nut, and 

 commonly in Conifers, Cycas, the Onion, and the Mistletoe. 

 Now and then a union takes place of these embryos. 



It is distinguished into three parts ; viz., the radicle (Plate 

 VI. fig. 2. b, &c.) (rhizoma or rostellum] ; cotyledons* (fig. 2. 

 0, &c.) ; and plumule (or gemmule] (fig. 2. c.) ; from which is 

 also by some distinguished the cauliculus or neck (scapus, 

 scapellus, or tigelle] . Mirbel admits but two principal parts ; 

 viz., the cotyledons, and what he calls the blastema, which 

 comprises radicle, plumule, and cauliculus. 



The direction of the embryo is either absolute or relative. 

 Its absolute direction is that which it has independently of 

 the parts that surround it. In this respect it varies much in 

 different genera; it is either straight (Plate VI. fig. 5.), 

 arcuate (fig. 9.), falcate, uncinate, coiled up (fig. 8.) (cyclical), 

 folded up, spiral (fig. 19.), bent at right angles (Plate V. fig. 

 28.) (gnomonical, Link), serpentine, or in figure like the letter 

 S (sigmoid). 



* Cotyledon (KoruATjSwp), not cotyledon as it is often called. 



