PREFACE. 



XV 



But the absorption of fluid does not take place either by all the surface of their 

 roots, nor even of their fibres, but only by the extremities of the latter, consisting 

 of bundles of vessels surrounded by cellular tissue in a very lax spongy state, 

 whence those extremities are called spongioles. That it is only through the 

 spongioles that absorption to any amount takes place, is easily shown by grow- 

 ing a plant in water, and alternately preventing the action of the spongioles, 

 when languor and a cessation of vital action comes on, and preventing the action 

 of the general surface of the roots, leaving the spongioles at liberty, when the 

 vital energies are immediately renewed. These spongioles are exceedingly 

 delicate in their organization, and a very slight degree of violence destroys them. 

 It is scarcely possible to remove the soil from the roots without injuring them in 

 some degree, and if transplantation is effected violently or carelessly, they are in 

 a great measure destroyed. In proportion to the size or age of a tree, is the 

 difficulty of preserving them increased ; and hence at the same time the difficulty 

 of transplantation is augmented. If, by any method, the spongioles could be 

 preserved unharmed, there would be no reason whatever why the largest forest 

 tree should not be removed as easily as the young plants in a nursery ; but their 

 preservation in such cases is impossible, and therefore the transplantation of 

 trees of great magnitude cannot be effected. It is because of the security of the 

 spongioles from injury when the earth is undisturbed, that plants reared in pots 

 are transplanted with so much more success than if taken immediately from the 

 soil. Hence, also, when earth is frozen into a huge ball around the root of a 

 plant, transplantation is effected with the same kind of certainty. The practice 

 of cutting the roots of large trees the year previous to removing them is attended 

 with success for a similar reason. Wherever the roots are cut through, the new 

 fibres which are emitted, provided a plant is in health, in short tufts, and each 

 terminated by a spongiole, are much more easily taken out of the ground without 

 injury than if they were longer and more scattered among the soil. When 

 destroyed, the spongioles are often speedily replaced, particularly in orchard 

 trees, provided a slight degree of growth continues to be maintained. This is 

 one of the reasons why trees removed in October succeed better than if trans- 

 planted at any other time. The growth of a tree at that season is not quite 

 over ; and the first impulse of nature, when the tree finds itself in a new situa- 

 tion, is to create new mouths by which to feed when the season for growing 

 again returns. 



" Evaporation takes place in plants to an inconceivable degree in certain cir- 

 cumstances. It is known by the experiments of Dr. Hales, that a sunflower 

 plant will lose as much as 1 lb. 14oz. by perspiration in twelve hours; and that 

 in general, " in equal surfaces and equal times, a man would perspire 3^, the 

 plant Y^j, or as 50 : 15;" and that taking all things into account, a sunflower 

 perspires 17 times more than a man. The same most accurate observer found 

 that a cabbage perspired in twelve hours 1 lb. 9oz. ; a Paradise Stock in a pot 

 1 loz. ; and a Lemon Plant, 8oz. Guettard states that he found Cornus Mascula 

 perspire twice its own weight in a day; and Mr. Knight has remarked a Vine 

 in a hot day losing moisture with such rapidity that a glass placed under one of 

 its leaves was speedily covered with dew, and in half an hour the perspiration 

 was running off the glass. In damp or wet weather this evaporation is least; 

 in hot dry weather it is greatest. This loss has all to be supplied by the moisture 

 introduced into the system by the spongioles ; and hence, if the spongioles are 

 destroyed, and evaporation takes place before they can be replaced, a plant must 

 necessarily die. This is the reason why deciduous trees cannot be transplanted 

 when in leaf; it is impossible to remove them without injuring their spongioles, 

 and it is equally impossible to hinder the evaporation by their leaves : but if 

 they are kept in pots, it matters not at what season their removal takes place, 

 because as their spongioles are then uninjured, even excessive evaporation would 

 be made good by their action. It it is well known that certain evergreens, such 

 as Hollies, Laurels, &c. can be transplanted in almost all months ; this arises 

 from their perspiration being being much less copious than in diciduous trees, 

 wherefore the spongioles have less difficulty in supplying the loss occasioned by 

 it ; yet even evergreens cannot be removed in the hottest months in the year, 

 because then the action of such spongioles as may be saved in the operation 

 would not be sufficient to supply the waste by evaporation. Plants first begin- 



