PHYSIOLOGY OF VEGETABLES* 107 



often porous, variously perforated or torn. Of the 

 tubes, some are without any lateral perforations, b. 

 at least for a considerable extent ; others pierced with 

 holes ranged in a close spiral line, c. ; in others, sev- 

 eral of th^se holes run together, as it were, into inter- 

 rupted spiral clefts, d. ; and in some, those clefts 

 are continued, so that the whole tube, more or less, is 

 cut into a spiral line, e. ; which, in some young 

 branches and tender leaves, will unrol to a great ex- 

 tent, when they are gently torn asunder. The cellular 

 texture, especially, is extended to every part of the veg- 

 etable body, even into the thin skin, called the cuticle, 

 which covers every external part, and into the fine 

 hairs or down, which, in some instances, clothe the 

 cuticle itself. 



CHAP. III. 

 PHYSIOLOGY. 



Having, in the former chapter, given a brief outline 

 of the structure of the internal organs of plants, we pro- 

 ceed to give some account of the supposed functions 

 these perform. 



I. Division of a Plant into parts according to the func- 

 tions they perform. 



Every plant examined as to external structure dis- 

 plays at least four systems of organs. 1. The Root ; 

 2. the Trunk and Branches ; 3. the Leaves ; and 4. the 

 Fructification. Davy. 



1. The Root fixes the plant in the earth and imbibes 

 the nourishment from the soil. The root is a continu- 

 ation of the trunk, and is similar to it in its anatomi- 

 cal structure. While the trunk terminates in leaves, 

 the root terminates in fibres or radicles, in which its 

 peculiar functions are performed. 



2. The Trunk elevates the leaves, flow r er and fruit to 

 a convenient and proper situation, and serves as a me- 



