13-i Professor Alexander Dickson on the 



Chilian Amarjllids Alstraemeria, Bomarea, and LeontocMr, 

 and of the Liliaceous genera (curiously enough, also Chilian) 

 CaUixene and Luzuriaga, where the stomata are developed 

 exclusively on the morphological upper leaf-surface, which 

 ultimately becomes directed downwards by a twist ; and 

 various authors have noted the occurrence of a similar 

 condition in species of Allium, of Graininece, &c. 



The physiological problem afforded by these twisted 

 cladddes or twisted leaves is one of considerable difficulty. 

 At first sight we are disposed to wonder at an arrangement 

 where the stomata appear to be developed — so to speak — 

 on the wrong surface, to be set right afterwards by a 

 twist.* Of course, given a pale stomatic surface on the 

 morphological upper side, the twisting of the organ might 

 naturally be expected to occur : just as ordinary leaves tend 

 to right themselves by a twist, when their surfaces are 

 reversed artificially, by inversion of the plant or branch ; 

 or as in the familiar case of a plant grown at a window, 

 where the leaves so adjust themselves that the stomatic 

 surface is directed away from the light. But why should 

 the stomata have been developed on the morphological 

 upper surface, instead of on the lower ? It may be assumed 

 that such a curious arrangement must be of some use to 

 the plant ; and, this premised, the question arises as to 

 whether it is the shifting of the stomata to the morpho- 

 logical upper side, or the twisting of the organ on itself, 

 that is the matter of primary physiological importance. As 

 regards the actual sequence of phenomena in the develop- 

 ment of the plant, there is no doubt that the formation of 

 the stomata on the morphological upper side precedes the 

 twisting of the organ, which only takes place when the 

 parts are set free by unfolding of the bud ; but I think 

 we may at once set aside the idea that the shifting of the 

 stomata to the morphological upper side is the matter 

 of primary importance, since it is scarcely conceivable 

 how such a shifting can of itself be of any service to a 

 plant, except, of course, in the case of one with its leaves 

 floating on the surface of the water. If, however, we look 



* An apparent paradox almost as great as that exhibited by the flower of 

 Malaxu iMla/l.o.ia, pointed out by Darwin, in which the labellum, instead of 

 becoming inferior by a half-twist of the ovary, as in ordinary Orchids, is 

 restored to its original superior jiosition by a whole twist. 



