494 REV. GEORGE HEN SLOW ON A THEORETICAL 



some days after its appearance. " II resulte de la que l'embryon 

 seminal du Tamme est ve'ritablement dicotyledon." The next 

 leaf is situate in a plane at right angles to that passing through 

 the cotyledons. The germination, Dutrochet observes, agrees 

 exactly with that of Asparagus. 



M. Ph. van Tieghem's observation, therefore, appears to afford 

 good reasons for suspecting that the presence of only one coty- 

 ledon is simply due to the partial or total arrest of the other. 

 I say partial, for in some cases considerable discussion has arisen 

 concerning the nature of the appendage to the embryo, opposite 

 to the single cotyledon of certain grasses*. Several botanists 

 regard this as a rudimentary cotyledon. M. Ph. van Tieghem's 

 objection to this view is based on the fact that it is devoid of 

 vessels ; but this does not seem to me to be of any weight, since, 

 as organs degenerate, so do the fibro-vascular cords tend to, or 

 quite disappear. Thus, while Primula has cords in the place of 

 the missing stamens, Rhamnus has none, though its stamens are 

 opposite to the petals, as in the former plant. Again, stipules as a 

 rule are provided with cords derived from the lateral members 

 of the vascular system of the petioles ; but in some desert 

 species of the lllecebracea, as Poly carp on sinaitica and Poly- 

 carpaa fray His, the scarious stipules have no trace of vessels of 

 any kind whatever. Again, a quadrangular papilla occupies the 

 position of the pistil in the male flower of box, and a conical one 

 in that of Lychnis dioica ; but the cords which should have been 

 supplied to the carpels stop short at some distance below it in 

 the former, and are totally wanting in the latter, &c. 



In fact, the presence of cords is a mere question of degree of 

 degeneracy ; and considering how feeble the cords are, even in a 

 cotyledon, their function being to convey nutriment to the 

 plumule and radicle, it is just what one would expect, to find 

 them totally absent, when there was no nutriment in the rudiment 

 at their disposal. 



Monocotyledonous" Dicotyledons. — The question arises, as- 

 suming a monocotyledon to have descended Irom a plant with 

 two cotyledons through an aquatic habit, do we find any instances 

 in support of this view, anions existing dicotyledons, which are 

 now aquatic, or have presumably descended from water-plants? 

 More than one order supplies us with such. Trapa natans, for 



u 



As in /Egilops, Oat, Lolium temulentttm, &c. 



