Organization of Leaves. lOSf 



pie, they are nearly spherical in the fritillaria, elongated or 

 cylindrical in the lavatera triloba and the erytkroiui/m dens 

 leonis, prismatic in the aloe, and ineguiar in the sijlphlum 

 perJoUahtm. 



The utriculi of the parenchyme of the same leaf are seen 

 to vary also in rcsard to their form and size. Thus the 

 leaves of the sijlfkium and the impatiens hahamina have 

 the utriculi irregular on the mfcrior side and cylindric on 

 tlic superior. I'hose of the nenuphar have them small and 

 elongated on the upper side, and large and prismatic on the 

 lower. Those of the narcissus and others of the lily kind 

 have them round and small on both sides, but large and 

 prismatic in the interior part of the leaf. 



From what has been said, if we suppose the parenchyme 

 of a leaf to be composed of spherical utriculi adhering to 

 each other, it will readily be conceived that, as these utriculi 

 cannot touch each other throughout their whole surface, the 

 necessary result will be vacuities or intervals between them, 

 •which will have a communication with each other, as seen 

 fig. 15. If the utriculi are irregular, as those of fig. 18, 

 the vacuities in this case will be larger ; and if the utriculi 

 approach the cylindric or prismatic form, the vacuities will 

 be the less sensible as the utriculi touch each other in a 

 greater extent of their surface. 



It is of importance to comprehend properly the'aggre^a- 

 tion of the utriculi ; the vacuities resulting from it, which 

 in future I shall call utricular interstices ; and the commu- 

 nication of these utriculi with the pores, in order to account 

 for the circulation of the air in the leaves. 



That air exists in leaves is a truth fully confirmed ; for, 

 by compressing them in water, the air is seen to issue from 

 them. By exposing them under water to the action of an 

 air-pump they emit air; and if they be left in the water tor 

 tome time they soon lose their opacity, become transparent 

 by the introduction of water, which assumes the place of 

 the air, and are precipitated to the bottom of the vessel. 

 In a word, these leaves when again exposed to the air gra-- 

 dually resume their opacity and ;hen- natural colour; which 

 can be ascribed only lo the air which re-enters as the water 

 13 evaporated. But where is this air lodged? I shall reply 

 from my observations, tha.t it is contained in the utricular 

 interstices of the parenchyme. 



If a leaf of the friilUuria or the pnrtnlnca be examined 

 with the naked eye, or, still better, with a magnifying glass, 

 there v.i!l be observed m its interior part small luminous 

 poiuls, which are produced by the air contained in the utri- 

 cular 



