APPENDIX 



PHYSIOLOGICAL 



The ordinary cultivated plants, all except the mushrooms, 

 absorb water and all needed nutrients, except carbon, through 

 the roots. The absorbing organs are very fine 

 root hairs (Fig. 203), located near the extreme 

 root tip. From the point of absorption the 

 crude foods must be distributed to the plant 

 parts where they are to be utilized; that is, 

 largely to the parts that are growing and to any 

 green part. This necessitates a conducting sys- 

 tem which exists in the veins continuous through- 

 out the plant, consisting of microscopic water 

 ducts (Fig. 206) extending through the wood of 

 the root, stem, and leaf. The upward sap cur- 

 rent passes through these ducts. A living plant 

 is constantly giving off water, transpiring. The 

 amount is considerable, averaging 75 kilo, daily 

 for a full size beech tree. This water too must 

 rise through the ducts. 



Any injury of the root hairs retards absorp- 

 tion, and any stoppage or interruption of the 

 ducts in root or stem hinders the rise of sap, 

 and in either case poor nutrition or even wilting 

 may result. 



The carbon necessary for the plant is derived from the air, 

 taken in mainly through the stomata (Fig. 205, epidermal 



483 



Fig. 203. — Plant- 

 let showing lo- 

 cation of root 

 hairs near the 

 root tip. 



