EXO 



C 382 ] 



EXT 



E. longiflo'rum (long-flowered). 30. White 

 June. Caraccas. 1820. 



EXOTICS. Plants belonging to 

 country different from that in which 

 they are growing. 



EXTRAVASATED SAP may arise from 

 five causes. 



1. The acrid or alkaline state of the 

 sap, which has been considered already, 

 when treating of the Canker. 



2. Plethora, or that state of a plant's 

 excessive vigour in which the sap is 

 formed more rapidly than the circu- 

 latory vessels can convey it away. 

 When this occurs, rupture must take 

 place. If the extravasation proceeds 

 from this cause, there is but one course 

 of treatment to be pursued, root- 

 pruning, and reducing the staple of 

 the soil, by removing some of it, and 

 admixing less fertile earthy compo- 

 nents, as sand or chalk. This must 

 be done gradually, for the fibrous roots 

 that are suited for the collection of 

 food from a fertile soil are not at once 

 adapted for the introsusception of that 

 from a less abundant pasturage. Care 

 must be taken not to apply the above 

 remedies before it is clearly ascertained 

 that the cause is not an unnatural con- 

 traction of the sap vessels, because, in 

 such case, the treatment might be in- 

 jurious rather than beneficial. We 

 have always found it arising from an 

 excessive production of sap, if the tree 

 when afflicted by extravasation pro- 

 duces at the same time super- luxuriant 

 shoots. 



3. Local contraction of the sap ves- 

 sels. If the extravasation arises from 

 this cause, there is usually a swelling 

 of the bark immediately above the 

 place of discharge. In such a case the 

 cultivator's only resource is to reduce 

 cautiously the amount of branches, if 

 the bleeding threatens to be injuriously 

 extensive, otherwise it is of but little 

 consequence, acting, like temporary 

 discharges of blood, as a relief to the 

 system. 



A. The extravasation of the sap from 

 a wound is usually the most exhaust- j 

 ing, and as the wound, whether con- : 

 tused or cut, is liable to be a lodgement | 

 for water and other foreign bodies op- 

 posed to the healing of the injured 



part, the discharge is often protracted. 

 This is especially the case if the wound 

 be made in the spring, before the leaves 

 are developed, as in performing the 

 winter pruning of the vine later than 

 is proper. In such case, the vine always 

 is weakened, and in some instances it 

 has been destroyed. 



5. Heat attended by dryness of the 

 soil, as during the drought of summer, 

 is very liable to produce an unnatural 

 exudation. This is especially notice- 

 able upon the leaves of some plants, 

 and is popularly known as honey-dew. 

 It is somewhat analogous to that out- 

 burst of blood, which in such seasons 

 is apt to occur to man, and arises from 

 the increased action of the secretory 

 and circulatory system to which it af- 

 fords relief. There is this great and 

 essential difference, that, in the case of 

 plants, the extravasation is upon the 

 surface of the leaves, and in proportion 

 consequently to the abundance of the 

 extruded sap are their respiration and 

 digestion impaired. 



Azaleas sometimes, but rarely, have 

 the hairs on their leaves, especially on 

 their lower surface, beaded as it were 

 with a resinous exudation. This can 

 scarcely be called a disease. It is never 

 found but upon plants that have been 

 kept in a temperature too high, and in 

 a soil too fertile. It is an effort to re- 

 ieve the surcharged vessels, and occurs 

 n various forms in other plants. 



The various successful applications 

 of liquids to plants, in order to prevent 

 the occurrence of the honey-dew and 

 similar diseases, would seem to indicate 

 hat a morbid state of the sap is the 

 ihief cause of the honey -dew, for other- 

 wise it would be difficult to explain the 

 reason why the use of a solution of 

 common salt in water applied to the 

 il in which a plant is growing, can 

 )revent a disease caused by insects. 

 But if we admit that the irregular ac- 

 tion of the sap is the cause of the dis- 

 order, then we can understand that a 

 portion of salt introduced in the juices 

 of the plant would naturally have a ten- 

 dency to correct or vary any morbid 

 tendency, either correcting the too rapid 

 secretion of sap, stimulating it in pro- 

 moting its regular formation, or pre- 



