40 NUTRITION. 



buds universally originate in the horizontal or 

 cellular system." 



36. The nutritive organs of cellular plants are 

 far less defined than those of the vascular tribes, 

 and it even appears as if the whole mass of the 

 former were composed of one homogeneous sub- 

 stance, capable of taking diverse forms, and ful- 

 filling different functions, without being sepa- 

 rated into distinct organs. They are analogous 

 in many cases to those of vascular plants, but 

 never consist of vessels. They vary so much in 

 the different species of the cellular tribes, such 

 as the Mosses, Hepaticae, Lichens, &c. that it 

 would be impossible to describe them here with- 

 out entering into details far exceeding the limits 

 of this work. 



37. On considering the phenomena of vege- 

 table nutrition, one fundamental principle meets 

 us at the outset ; viz. that no aliment ever pene- 

 trates the plant, unless water serve it for a 

 vehicle. Without water there is no vegetation. 

 The first thing then to inquire is how it enters 

 into the system. The habitual and vital absorp- 

 tion of water is performed by the spongioles of 

 the roots (8), although under certain conditions, 

 such as rain, heavy dew, artificial watering, &c. 

 the surfaces of the leaves have also the power of 



