10 VEGETABLE PHYSIOLOGY. 



of the plant are elaborated its essential qualities. The 

 radicle fibre is a very delicate organ ; it appears to be 

 elongated by protrusion of its centre. The apex is 

 rather blunt, but a notable portion of its length is 

 thickly beset with hair-like appendages which are 

 probably absorbents. Fibres diverge from where they 

 are exserted in quest of humidity, naturally receding 

 from dry air, and turn from it whether it be above or 

 beneath them. They are not averse to light provided 

 it descends upon them through the medium of water 

 or very moist air. That such fibres are only ejected 

 in humid air, is evident from the circumstance of their 

 never appearing on roots produced in the air, as those 

 of Epidendrum, Pandanus, and many other plants ; 

 from which it may be inferred, that when such organs 

 are destitute of fibres they are furnished with ab- 

 sorbent valves, or stomata, to admit nutritious fluids 

 from the atmosphere. 



The growth of fibres is simultaneous with that of 

 the other parts of the system ; each additional shoot 

 above requires in its development the assistance of 

 new fibres below. But their powers and properties 

 will be more fully adverted to when we come to 

 describe the under-ground stems of plants. 



Conducting Organs. All vegetable structure is 

 permeable to currents of fluids. In the lowest grade 

 of cellular es, water seems to be transfusible in any 

 direction throughout the whole mass of the plant, as 

 we see it is in a bit of common sponge. In the 

 higher orders of vasculares, the cellular frame is 



