ON THE TORPIDITY OF PLANTS. 166 



Not only do the seasons effect a change in the leaves and the other 

 oi-gans of a plant which are above ground, but a change is also effected 

 in the condition of the roots. As the leaves are the organs which per- 

 form the functioa of evaporation, they having fallen, evaporation is 

 DOW almost suspended, with the exception of what little moisture 

 may exude through the bark ; the function of absorption, therefore, 

 will cease to be carried on with activity, which function, as is well 

 known, is performed by the extremities of the roots or spongioles. 



In autumn, I have said, the plant is very much in the condition 

 of the hybernating animal, the root and pulp wood are supplied with 

 a larger proportion of nutrient pulp than usual, and thus it is that all 

 the parts are dry and solidified ; the roots themselves are firm and not 

 liable to be easily broken, but the sjiongioles are absent, their func- 

 tion being no longer required until the ensuing spring. 



These spongioles are the pulpy and bibulous extremities of the fine 

 fibres of roots, and are so called from their absorbing like little sponges 

 the moisture of the soil. They are composed of one or more central 

 ducts or vessels, enveloped by a cellular tissue, but they are not like 

 other parts of the root covered by an epidermis or skin. 



It is in autumn, then, that both theory and practice direct us to 

 transplant trees. At that season every circumstance concurs to render 

 the operation practicable; but if we wait until the spring the 

 spongioles are likely to be destroyed, and many causes may call the 

 already turgid plant into growth, before the roots have had time to 

 form new spongioles. 



Observation and experience shews us that periods of growth and 

 repose are essentially necessary to the well being of plants, and that 

 by placing them in circumstances however favourable to prevent this 

 change in condition, it is scarcely possible so to do. But if it ever 

 does occur that this change in condition is prevented, it is never 

 done without the plant falling a victim to the unnatural position in 

 which it is placed. 



Nor is the repose from the effects of light less necessary for the 

 well-being of a plant, than from the urmatural stimulation above 

 alluded to. If plants were kept continually exposed to the rays of 

 white light, they would be always decomposing carbonic acid, and 

 would in consequence become so stunted, that there would be no 

 such thing as a tree, as is actually the case in the polar regions. If, 



