VEGETATIVB OKGANS OF PLANTS. 281 



garden soil, sand, moss, or charcoal, and after they had 

 attained considerable growth, removed the earth, etc., 

 from their roots by washing with water, using care not 

 to injure 6r wound them, and then immersed the roots 

 in Tessels of pure water. The plants were allowed to re- 

 main in these circumstances, their roots being kept in 

 darkness, but their foliage exposed to light, from three 

 to seventeen days. In most cases they continued appa- 

 rently in a good state of health. At the expiration of 

 the time of experiment, the water which had been in 

 contact with the roots was evaporated, and was found to 

 leave a very minute amount of yellowish or brown mat- 

 ter, a portion of which was of organic and the remainder 

 of mineral origin. Dr. Gyde concluded that plants do 

 throw off organic and inorganic excretions similar in 

 composition to their sap ; but that the quantity is ex- 

 ceedingly small, and is not injurious to. the plants which 

 furnish them. 



In the light of newer investigations touching the 

 structure of roots and their adaptation to the medium 

 which happens to invest them, we may well doubt 

 whether agricultural plants in the healthy state excrete 

 any solid or liquid matters whatever from their roots. 

 The familiar excretion of gum, resin, and sugar* from 

 the stems of trees appears to result from wounds or dis- 

 ease, and the matters which in the experiments of Gyde 

 and others were observed to be communicated by the 

 roots of plants to pure water probably came either from 

 the continual pushing off of the tips of the rootlets by 

 the interior growing point — a process always naturally 

 accompanying the growth of roots — or from the disor- 

 ganization of the absorbent root-hairs. 



Under certain circumstances, small quantities of sol- 

 uble salts or free acids may indeed diffuse out of the 



*From the wounded bark of the sixgar-pine (Pimfs Lambertiana) of 

 California. 



