86 TWELFTH REPORT. 



PLANT EXCRETION. 



J. B. DANDENO. 



By exci^tion is meant the process involved in the setting aside of 

 useless or harmful products, either within or without the cells of the 

 tissue concerned. In a general way, the excretory products of plants 

 are found in one or more of the following places: (1) in intercellular 

 spaces, (2) in vacuoles of cells, {3} in cells from which all other content 

 has been withdrawn, (4) on the outside entirely of the plant, (5) in 

 glands. Excretory products may occur (1) as liquid in glands or in the 

 vacuoles of cells, (2) as solids (crystals), (3) as gases set free from 

 the walls of the cells of living tissues. 



The metabolism of plants is so complicated and so variable that a 

 great variety of forms of excretory products is to be expected, depending 

 on the character of the plant, and upon the external and internal condi- 

 tions. The character of the plant is the chief factor in deciding as to 

 what the substance of the excretion may be. The external conditions 

 have to do more particularly with the location of the excretory sub- 

 stance. 



The matter of excretion in short-lived plants like Spirogyra, Pleu- 

 rococcus, etc., is exceedingly simple, the product being attracted from the 

 vacuole by the surrounding water, if the vacuole itself is insufficient to 

 contain it. In tJie case of long-lived plants, such as trees, the process 

 becomes much more complicated, and at the same time a nmtter of more 

 importance. But the tree has several means, in a general way, by which 

 the process of excretion is carried on. These are the dead cells, corky 

 bark, leaves (which are only temporary structures and consequently are 

 lost sooner or later carrying with them the excretion), mycorrhiza which 

 feed upon the excretions made by rootlets of long lived trees and shrubs, 

 glandular structures and surfaces. 



The functions of excretions if they have any, must be more or less 

 indirect, as for exam])le, in the cases of poisonous or malodorous sub- 

 stances which upon occasion serve the purpose of protection against 

 certain enemies. Resin, which is thought to be an excretion, may prove 

 of advantage to the plant upon the occasion of mechanical injury-, acting 

 as an antiseptic to the wound. 



Several other substances which are claimed to be absolutely essential 

 to the plant are supposed by some to be primarily excretory. Take for 

 instance, the cellulose cell wall. Some very low fonus of plant life ai*e 

 devoid of a cellulose wall, and it does no violence to our ideas of the 

 cell to su]>pose that cellulose being no longer of use in the metabolism 

 of the protoplast was deposited laterally and externally as a wall, this 

 wall proving at the same time to be useful in protecting the cell against 

 several injurious conditions, e. g. loss of water. This is probably an 

 extreme view, but it illustrates the point. If the cell wall be an excretory 

 product, this is a case where the excretion becomes not only important 

 but of essential importance. 



