730 PHYSIOLOGY. 



sorption. 5. Simple wasliing with distilled water, and more 

 especially with soap and water, augments the absorptive power. 

 6. When the epidermal tissues of leaves have lost their power of 

 absorbing water, they can still absorb carbonic acid. 



5. Functions of the Intercellular System — The intercel- 

 lular canals, except in those cases in which the tissues of the plant 

 are gorged with sap, as in the spring of the year, are filled with 

 air, and the especial function which they perform is, to allow a 

 communication between the external air and the contents of the 

 internal tissues by virtue of the laws regulating the diffusion of 

 gases. They also facilitate exhalation of liquid matters by their 

 connection with the stomata. The intercellular spaces are also, 

 in most cases, filled with air ; while the air-cells and cavities, as 

 their names imply, are in like manner filled with aeriform 

 matters, and in water plants, are especially designed to diminish 

 the specific gravity of the parts in which they are found, and 

 thus to enable them to float readily. The receptacles or reservoirs 

 of secretion, as their name implies, contain the peculiar secretions 

 of certain plants, and are hence closely allied in their nature to 

 glands. 



Section 2. — Physiology op the Organs of Nutrition or 

 Vegetation. 



1. Of the Root or Descending Axis. — The oflSces performed 

 by the root are: — 1. To fix the plant firmly in the earth or to 

 the substance upon which it grows, or in some cases, as in many 

 aquatic plants, to float it in the water ; 2. To absorb liquid food ; 

 3. According to some authors, to excrete into the soil certain 

 matters which are injurious, or at least not necessary for the 

 healthy development of the plant ; 4. To act as a reservoir of 

 nutriment. 



The office which the root performs of fixing plants in those 

 situations where food can be obtained, is evident, and needs no 

 further remarks. It is also essential to the proper performance 

 of its absorptive powers. 



Absorption by the Boot — The function which the root performs 

 of absorbing nutriment for the uses of the plant, from the ma- 

 terials in or upon which it grows, is not possessed by its whole 

 surface, but is almost exclusively confined to the cells and 

 fibrils (Jig. 232) of the newly developed portions and young 

 parts adjacent to them. Hence, in the process of transplanting, 

 it is necessary to preserve such parts as far as possible, otherwise 

 the plants thus operated upon will languish or die, according to 

 the amount of injury they have sustained. The injury done to 

 plants in transplanting, is also to a great extent influenced by 

 atmospheric circumstances and conditions of the soil at the time 

 in wliich such an operation is performed ; thus, under the favour- 



