66 CONIFEROUS GLANDS GUILLEMIN. [BOOK i. 



trees. At Plate II. fig. 20. is a view of it as I see it in 

 Sphserostema. 



The nature of the discs has been examined by the late M. 

 Guillemin, who, in a paper laid before the Academy of 

 Sciences, Dec. 19, 1836, considered them to be tumours, and 

 called them (Edemata. He supposed them to be flattened 

 vesicles, the central circle being either a pore or minute cell ; 

 and he imagined them to be filled with a colourless volatile 

 oil, which changes to turpentine when it has been excluded 

 from the central luminous point. He also adverted to the 

 existence of similar appearances in aromatic woods, especially 

 Drimys chilensis, but said they are not to be confounded 

 with (Edemata. (Comptes Rendus, iii. 761.) There is, how- 

 ever, no sufficient ground for regarding them as organs of 

 secretion ; it is more probable, considering their position, 

 that these circles are analogous to the pits of bothrenchym, 

 and are intended to enable fluid matter to pass in or out of 

 the tubes, which could scarcely take place, except in an incon- 

 siderable degree through their tough thick sides. 



The late Mr. E. J. Quekett has given the history of coni- 

 ferous glands so well, that I extract his observations from the 

 Linnean Transactions, vol. xix. p. 150. "The other point 

 that has occasionally been the subject of controversy, is the 

 nature of the discoid bodies on the woody tissue of coniferous 

 plants. These have been supposed by some persons to be 

 glands ; by others to be thicker, and by others again to be 

 thinner places in the membrane forming the walls of the 

 woody fibres. Others have asserted that there is a pore in 

 the centre of each disc, which allows of a communication 

 between adjoining fibres. Later observers, however, have 

 shown that none of the above theories are altogether correct, 

 as the discs are not proper to one woody fibre, but are formed 

 between two contiguous fibres, each contributing to the for- 

 mation of the disc by having a minute depression shaped like 

 a saucer, on its exterior, which corresponds exactly to a similar 

 depression on the contiguous fibre, whereby a small cavity is 

 left between them. These markings or cavities very rarely 

 exist on the sides of the fibres opposed to the pith or bark, 

 but are very numerous on the sides parallel to the medullary 



