178 



SCIENCE OF GARDENING. 



II. 



it is the model and proto* 

 type. The natural graft is 

 always affected by means 

 of the union of the liber of 

 the respective stems com- 

 posing it ; so that the per- 

 fection of the art of grafting 

 consists in applying the liber 

 of the graft and stock toge- 

 ther in such a manner as 

 shall most facilitate their 

 incorporation. 



793. If the branch of 

 a tree is situated as in 

 the foregoing case of 

 the stem, so as to be 

 partially or periodically 

 immersed in water, it 

 will send out also the 

 same sort of brush-like 

 shoots. 



794. Bunches or knots, 

 exhibiting a plexus of young 

 shoots (Jig. 59 . a) issuing 

 from nearly the same point, 

 crossing in all directions, 



and finally incorporating together by means of a sort of natural graft, frequently disfigure it. These bunches 

 are frequently to be met with on the branches of the birch-tree, and are known among the peasantry of Scot- 

 land by the name of witches' knots. They are occasioned, like the bunches of the stem, by some obstruc- 

 tion in the channel of the sap or proper juice. A peculiar sort of knot or bunch is also often formed on 

 the branches of the dog-rose. The nucleus, which is generally from an inch to an inch and a half in 

 diameter is covered with a long and winged shag, first of a green and then of a purple color, presenting 

 the appearance of a small bunch of moss. {fig. 58. b) It has been occasioned like that of the stem of the 

 thistle, by the puncture of an insect depositing its eggs in the tender shoot ; for if it is cut open about the 

 month of August, its contains maggots. These anomalies remind us always of that singular disease in the 

 human species, the Plica polonica. 



795. The bud. The regular developement of the bud is also often prevented by means 

 of the puncture of insects, and converted into a large globular tumor. 



796. The gall tumor is very often effected by a species of Cynips that lances its piercer into the heart of the 

 bud while yet tender, and penetrates with its saw into the very pith ; injecting at the same time a drop of 

 the corroding liquor contained in its bag, and then laying its egg. The bud being thus wounded, and the 

 juices corrupted by the injected poison, the circulation is not only impeded, but a fermentation is induced 

 which burns the contiguous parts and changes their color. The extravasated juice flows round the egg, and 

 is there accumulated and converted into a sort of spongy lump which vegetates and augments till it forms 

 •what is called a gall. The gall thus formed affords both shelter and nourishment to the young maggot, 

 which, after being converted into a flv, pierces its enclosure and launches into the open air. The most re- 

 markable of such galls are those produced on the oak-tree, and known in this country by the vulgar 

 name of oak-apples, (fig. 59. b) The bud of the willow, particularly salix helix, is apt always to be 

 punctured by insects and converted into a gall. But the conversion is not always complete ; and in this 

 case the shoot remains dwarfish, and the leaves, which are now protruded from nearly the same point, 

 assume something of the figure of a rose. Hence it has obtained the common name of the rose-willow. 

 The galls of the salvia pomifera formed in the above manner arc said to be of a very pleasant flavor, and 

 are esteemed a great delicacy in eastern countries. 



797. The leaves, like the buds, are also frequently chosen for the nidus of in- 

 sects, and disfigured with galls or excrescences. But the most remarkable gall 

 produced on the leaf, and indeed the most remarkable and important of all galls, 

 is that which is so extremely useful in the arte of dyeing and making ink, the nut-gall 

 of the shops. 



