CHAPTEK II. 



VASCULARES, ORVASCULAB, FLOWERLESS PLANTS. 



99. Every plant germinating from the spore or seed has a 

 tendency to develop in three directions, upwards, downwards, 

 and horizontally, according to the nature of the tissues of which 

 it is composed. The fibrous and yasoular system is developed 

 vertically, in an ascending and descending direction, except- 

 ing in the case of the leaves, where it takes a horizontal 

 spread ; the cellular system, on the contrary, is developed for 

 the most part horizontally. In the lower tribes of crypto- 

 gamic plants, the structure is wholly cellular, and the plants, 

 therefore, are wholly stemless and leafless, the greater part 

 of them consisting of flat expansions of vegetation, spreading 

 centrifugally in one plane, increasing by additions of cellular 

 matter to their periphery or circumference, so as to form 

 a thallus, or bed of vegetable matter; hence these plants have 

 been called Thallophytes (eaj.>.05 a frond, and ^vtov a plant). 



100. In the higher tribes of cryptogamio plants, the fibrous 

 and vascular tissues enter into the composition of their structure, 

 and these plants necessarily develop vertically as well as horizon- 

 tally. These two systems of tissue, I mean the vascular and 

 fibrous vertical system and the horizontal cellular system, 

 cross each other at right angles, become interwoven with each 

 other, and form a common axis of vegetation or stem. Part 



