176 PHYTONOMY. 



273. 



The sides of the cellular texture are, for the most part, 

 very thin, but yet completely impervious ; so much so, that 

 the communication of the sap from one cell to another can 

 only be explained by the supposition of an organic perspira- 

 tion. Yet there are exceptions to this. The cells of the 

 Epidermis are observed to have peculiar slits, (Tab. V. 

 Fig. i^.), of which we shall speak more particularly when we 

 treat of leaves ; and in Pines the extended cells are distinct- 

 ly observed to have gaps, which are surrounded by a pretty 

 high margin ; (Tab. V. Fig. 4.) 



The function of the cellular texture is simply to contain 

 and to prepare the sap. It is not destined to conduct up- 

 wards the unprepared sap, because in the bark and in the 

 pith, both of which have a structure entirely cellular, the as- 

 cent of the sap is not perceived. There are, however, what 

 have been called sap-vessels in the cellular texture, but these 

 originally are nothing else but extended cells, which are 

 often stretched to a considerable length. 



B, On the Sap-Tubes. 



274. 

 The second primitive form of all plants is the tube-form, 

 appearing to the unassisted eye like straight-lined fibres. 

 But by magnifying them we perceive that these apparent 

 fibres have a real, though uncommonly small diameter ; that 

 they are therefore real tubes, which proceed for a consider- 

 able length with a cylindrical shape, and are sharply pointed 

 at both ends; (Tab. V. Fig. 1.) 



275. 



Apparently these tubes are the perfect state of the second 

 common primitive form of organic bodies, namely, the right 

 lined. Because, althovigh they more frequently occur than 

 the third or spiral form, they arc later in being produced, 

 and are first observed, as we have said, in the Nematomyci, 



2 



