210 VEGETABLE ORGANOGRAPHY. 



those of leaves; most, however, are entire; but some 

 are lobed either at the apex, as in Helicteres, Convol- 

 vulus, the Radish, &c, or at the base, as in Polygonum, 

 &c. ; some are divided, being palmate, as in the Lime- 

 tree, or pinnatifid as in the Erodium Pimpinellifolium. 

 But the principal difference which they present in this 

 respect consists in the lateral cotyledons of phaneroga- 

 mous Monocotyledons being almost all sheathing at the 

 base, whilst this form is rare in Dicotyledons ; this cor- 

 responds very well with the ordinary form of the leaves 

 of the two classes. 



Among Dicotyledons, it happens from time to time 

 that the two cotyledons are found united ; this union 

 takes place laterally, unequally, and purely accidentally, 

 in a great number of plants — for example, in Ebenus 

 Cretica or Tithonia; it is constant and regular, in some 

 united at the base, so that they seem to form a kind of 

 disc pierced by the stem, as is seen in several Ficoids. 



Fleshy cotyledons are generally of a more irregular 

 form, and frequently united together by their whole 

 inner surface ; this is seen in the seeds of the Horse- 

 chestnut, Nasturtium, Eugenia, See, which at first sight 

 might appear Monocotyledons, because their two coty- 

 ledons are united into a single mass. 



The inequality of the cotyledons, which is rare and 

 entirely accidental in Dicotyledons, where they are foli- 

 aceous, is not very rare in those where these organs are 

 fleshy ; the seeds which I have mentioned present good 

 examples: but in this respect the seed of Trapa deserves 

 mention. In Trapa natans, which is so well known in 

 Europe under the name of Water-chestnut, the two 

 cotyledons are extraordinarily disproportionate; they are 

 exactly opposite, as in all Dicotyledons, but one is so 

 small, that it must be carefully sought for before it can 

 be .perceived, and it comes out without difficulty -with 



