30 TIITRD REPORT — 1833. 



I have endeavoured to show * that they are glands of a pecu- 

 liar figure, which stick to the sides of the tubes ; and I have 

 ascertained that the large round holes that are certainly found 

 in coniferous tissue are caused by the dropping or rubbing off 

 of such supposed glands. But a very different opinion is en- 

 tertained by Dr. Mohlf, whose observations have been con- 

 firmed by Dr. Unger;}:. In the opinion of the former of these 

 botanists the supposed glands of coniferous tissue are circular 

 spaces where the membrane of the tube becomes abruptly ex- 

 tremely thin ; and it is said that transverse slices of coniferous 

 wood, made at an angle of forty-five degrees, demonstrate the 

 fact. Dr. Mohl is also of opinion, as has been already said, 

 that the porous appearances above mentioned, and ascribed to 

 the adhesion of amylaceous matter to the sides, are of a similar 

 nature. 



It has been shown by Mr. Griffiths, that in the kind of tissue 

 called the dotted duct, the suspicion of Du Petit Thouars that 

 this form of tissue is composed of short cylindrical cells placed 

 end to end, and opening into each other, is correct ; their com- 

 munication, however, is not by means of an organic perfo- 

 ration, but is produced by the absorption and rupture of the 

 ends which come in contact. Mr. Slack has also stated, 

 in a very good paper upon Vegetable Tissue §, that in other 

 cases the vessels of plants open into each other where they 

 come in contact ; as, for example, at the conical extremities, 

 where ducts join each other ; but he represents this to be owing 

 to the obliteration of their membrane at that point ; the internal 

 fibre, of which they are in part composed, remaining like a 

 grating stretched across the opening where the enveloping 

 membrane has disappeared. 



In a short paper, published in the Journal of the Royal In- 

 stitution in December 1831, I have endeavoured to show that 

 membrane and fibre are to be considered the organic elements 

 of vegetable tissue, contrary to the more usual opinion that 

 membrane only is its basis : this was attempted to be proved, 

 not only by the fact that the simple cells of the testa of Mau~ 

 randia, &c., are apparently formed by a fibre twisted spirally 

 in the inside of their membrane, but also by the elastic spires I 

 had discovered on the outside of the seed of Collomia, in which 

 it is plain that no membrane whatever is generated. 



* Introduction to Botany, p. 16. t. 2. f. 7. 



t Ueher die Poren des Pjiemzen-Zellgeivehes. 



X Botanische Zeittmg, October 7, 1832. 



§ Transactions of the Societij of Arts, vol. xlix. 



