36 PROGBESS OF MICROSCOPICAL SCIENCE. 



present on their surface furrows corresponding to the spiral lines 

 which jut out from the walls of the vessel, and even little projections 

 corresponding to the cavities. It is then very certain that, in this 

 case, the gum is deposited in the interior of the vessels, and has taken 

 the impression of the interior. This gum is of the same nature with 

 that M. Trecul calls cerasone. 



2. Production in Cells. — Transformation of Starch. — Gum is often 

 seen in the medullary rays and there offers particular interest, 

 because its appearance is connected \vith the disappearance of the 

 starch originally contained in the cells. The cliange of starch into 

 gum has been noted by former observers, but never to my notion 

 precisely described. On the first appearance of gum in the cell, the 

 grains of starch, still entire, are gathered into little groups, aroimd 

 which appears a thin layer of gum, also small portions of which may 

 be seen deposited in other parts of the cell. The masses of starch 

 enveloped by gum diminish continually as the layer of gum increases 

 in thickness, but when treated by iodine the two substances preserve 

 their special properties without modification till the starch finally 

 disappears, usually leaving a small cavity in the centre of the little 

 mass of gum. When the production of gum commences in the tissues, 

 an increased amount of starch is observable in the neighbouring cells 

 which seems absorbed, and immediately changed into gum, but ordi- 

 narily the gum in this case does not ai)pear to be deposited in the 

 cells, but passes into the neighbouring reservoirs, where it accumu- 

 lates in considerable quantity. 



3. It is neither in vessels nor cells, but rather in the lacunae formed 

 in the interior of young tissues, the voluminous masses of gum accu- 

 mulate, which we often observe. These lacunae are most frequently 

 found in the cambial zone, but may be seen at diflerent depths in the 

 wood, disposed concentrically like successive annual layers. They 

 are formed in the germinal layer, and then occupy the interval between 

 the medullary rays. When not too largely developed, a new woody 

 layer forms outside of them, and the growth is not sensibly altered. 

 On the contrary, if growth cease at this point, a flow of gum is caused, 

 the woody tissue necroses and cannot be covered except by the extension 

 of lateral portions where the germinal layer is uninjured. 



The tissues next to these lacunae suffer an important modification of 

 development ; the cambium, instead of forming woody tissue, produces 

 cells in which an abundance of starch is deposited. There arises then, 

 wherever gum is developed, a particular tissue (woody parenchyma) 

 which does not exist in healthy stems, and whose appearance is so 

 intimately connected with the morbid formation of gum, that it may 

 be considered as a pathologic tissue. The starch, which accumulates in 

 this special woody parenchyma, is used, as in the medullary rays, to 

 form gum, which accumulates in large quantities in the lacuna?. These 

 lacunae increase at the expense of the neighbouring tissue, which is 

 disorganized; nevertheless, the cells which border the lacunae often 

 manifest extreme vital activity, and give birth to true pathologic 

 formations. They develop, multiply and ramify in the interior of the 

 lacunas, even when separated from the rest of the tissue, and absolutely 

 isolated in the middle of the gum. 



