20 



ORGANOGRAPHY. 



BOOK I. 



if tlie tissue of Zamia be allowed to remain maceratinsf for 

 some time in dilute nitric acid, the apparent pores disappear : 

 that is to say, the granules that cavise the appearance of per- 

 forations are dissolved. It has been thought that such ap- 

 pearances as these were confined to Cycadeas and Coniferte ; 

 but I suspect that they are far from uncommon in other fami- 

 lies. Such tissue constitutes a considerable part of the wood 

 of Calycanthus (Plate 11. fig. 4.), as has been already noticed: 

 and it is abimdant in Bragantia. This kind of tissue might 

 be called granular ivoody tissue : it approaches very nearly to 

 the character of vasiform tissue, into which, in Zamia, it seems 

 to pass by almost insensible transitions. It may, however, be 

 kno^\^l either by its very acuminated extremities, or by its 

 granules not being arranged in a spiral manner. 



3. The third kind of woody tissue is the glandular. This 

 has hitherto only been noticed in Coniferae, in which it is uni- 

 formly found in every species. Its dimensions are more con- 

 siderable than that of either of the last-mentioned forms; and, 

 like the second, it has been described as perforated with pores. 

 It differs from granular woody tissue in the markings of the 

 tubes being vesicular, and usually transparent, with a dark- 

 ened centre (Plate II. fig. 5, 6. 8.), which last is what has 

 been described as a pore, the vesicle itself being considered a 

 thickened rim. Kieser figures the glands as pores, both in Pine- 

 wood {fg. 4.), 

 and in Ephedra 

 {Jig- 5.), and in 

 other cases also. 

 They may be 

 most conveni- 



ently found by examining a thin shaving of common Pine- 

 wood (Pinus Strobus) with a microscope, when they will be 

 seen in the form of transparent globules, having a dark 

 centre, and placed upon the walls of the tissue. That these 

 globules are not pores, seems to me to be proved thus : they 

 are flaccid when dry, and distend when moistened, which is 

 not the property of a pore; their centre is more generally 

 opaque than transparent, which is also not the property of a 

 pore; they may be torn through die middle widiout any hole 



