Orgaiuzation of Leaves. 1 .3 



pressing the pores with a fine needle, which restored to 

 them their transparency. Are these bubbles atinosphcric 

 air, or a peculiar air produced by the plant itself? Tiie 

 following experiment may serve as an answer to this ques- 

 tion. 



I examined different pellicles taken from the surface of 

 the leaves. I ^uccessively compressed the pores, and al-* 

 ways observed the bubbles of air which issued to decrease 

 gradually in volume, and at length disappear entirely. Whe- 

 ther they remained attached to the utncuke, or to the point 

 of the needle, or whether they rose to the surface of the 

 water in which these pellicles were immersed, is not the 

 absorption of this air by water peculiar to carbonic acid 



cas 



Hedwig entertained no doubt that the pores had the fa-- 

 culty of being able to shut themselves, to oppose the intro- 

 duction of the floating particles disseminated in too great 

 quantity throughout the atmosphere. 



Krocker asserts* that the contraction of the pores of the 

 leaves of the amaryUis formosissbna takes place in a very 

 evident manner ; which induced me to examine this fact. 

 For this purpose I placed in the focus of the nrieroscope a 

 fragment of the pellicle of one of these leaves, moistening 

 it sufficiently to obviate its desiccation, and I viewed it very 

 attentively without observing any contraction in the pores ; 

 but having substituted for it another fragment of pellicle, 

 placed dry on the glass, I then saw the pores gradually con- 

 tract and close themselves entirely ; which I can ascribe only 

 to the shrinking of the conjugate utriculae, produced by the 

 evaporation of their juices : for, having moistened this pel- 

 licle, the pores gradually returned to their natural state. 



The result of this observation may give us an idea of 

 what the pores of vegetables may experience when exposed 

 to continued drought; and make us comprehend, at the 

 same time, the beneficent influence which rain and abun- 

 dant dews have on leaves. 



We have considered the pores and conjugate utricidae 

 under a general acceptation : let us now speak of an excep- 

 tion which relates to the family of the gramineous plants, 

 and which did not escape the acuteness of Hedwig. 



* De Plantarurn Epidermide — Specimen inaugurate, ^c, auctorr An- 

 tonio Krorkero. //rt/zr, iSoo, p. J I. Sjepins iipertas (rimas) majorcs in 

 planiib cotispexi. ijua; paiilo poft adhibito microfcupio, ipfaruni cot)trac« 

 tioncm evidcntiiriinc monflrabant. Obfciv^tori qujmvis ruiii, hoc pU^r 

 noiiiciion in fjlioruin tcnuium epidtimidc amarvllidii foiuiosiisiniaj^ 

 ^uain maxirac perfpicuum adparct. 



Th6 



