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external and internal galls, from their relations to the vegetable which 

 bears them. The first project outwards, and are only connected with 

 the plant by a very small peduncle ; the second kind are developed 

 within the tissues and organs they deform. 



External galls are sufficiently naturally divided into unilocular and 

 multilocular, from the number of cells which they contain. 



The unilocular class may be divided into five groups, whose struc- 

 tme is more and more simple as it recedes fi-ora the first type. This 

 type is represented by the large gall of commerce, and the French 

 gall. If taken when fully developed, they exhibit, from the surface 

 to the centre : — 



1. Epidermis without stomata. 



2. Cellular, subepidermal layer, analogous to the cellular tissue of 

 vegetables, containing colouring matter. 



3. Zone of irregular, ramose cells, with large cavities : the spongy 

 layer. 



4. Layer of hard, prismatic, dotted cells. 



5. Layer of very thick polyhedral cells, very hard, much dotted, and 

 forming the protecting layer to the nucleus. 



6. Central alimentary mass of soft cells filled with liquid ; the 

 external part containing starch-granules, colourable by iodine; the 

 internal, not producing this I'eaction. 



The central amylaceous mass disappears gradually during the deve- 

 lopment of the larva, which does not commence its metamorphoses 

 until it has consumed all the alimentary portion. 



May the most internal portion be regarded as fecula modified by a 

 process analogous to the commencement of digestion, or rather as 

 matter more specially azotized, serving for the first phases of embry- 

 otic development ? 



The French gall, like that of commerce, contains fibro-vascular 

 bundles, which pass from the point of insertion towards the centre, 

 and ramify in the interior of the parenchyma. We find in these bun- 

 dles, fibres, branching and dotted vessels, and true spiral vessels. 

 These disappear successively, and give the five groups of external 

 unilocular galls before mentioned. 



1. Hard and spongy : French gall, and gall of commerce. 



2. Hard : spherical galls, on oak-leaves. 



3. Spongy : cellular oak-galls, with regular tubercles. . 



4. Cellular : lenticular galls, on oak-leaves. 



5. Protecting layer disappears ; the subepidermic cellular tissue 

 only remains : spherical galls, on leaves of briar. 



