THE VEGETATIVE ORGANS OF PLANTS. 259 
it upon the observation that certain plants exude drops 
of liquid from their roots when these are placed in dry 
sand, and that odors exhale from the roots of other plants. 
Numerous experiments have been instituted at various 
times for the purpose of testing this question. The most 
extensive inquiries we are aware of, are those of Dr. Al- 
fred Gyde, (Zrans. Highland and Agr. Soc., 1845-7, p. 
273-92). This experimenter planted a variety of agricul- 
tural plants, viz., wheat, barley, oats, rye, beans, peas, 
vetches, cabbage, mustard, and turnips, in pots filled either 
with 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 in- 
jure or wound them, and then immersed the roots in ves- 
sels of pure water. The plants were allowed to remain 
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 apparently in a good 
state of health. At the expiration of the time of experi- 
ment, 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 matter, a portion of which 
was of organic and the remainder of mineral origin. Dr. 
Gyde concluded from his numerous trials, that plants do 
throw off organic and inorganic excretions similar in com- 
position to their sap; but that the quantity is exceedingly 
small, and is not injurious to the plants which furnish 
them. 
In the light of newer investigations touching the struc- 
ture of roots and their adaptation to the medium which 
happens to invest them, we may well doubt whether agri- 
cultural 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 
* From the wounded bark of the Sugar Pine, (Pinus Lambertiana,) of Cali- 
fornia. 
