Morpliology of Vegetable Tissues. By W. 11. Gilhuri. 809 



primary phloem and xylem, but a special and new tissue developed 

 from it ; that it arises in the layer of procambium which is next 

 adjoining the medulla or pith ; the cells composing the cambium 

 being developed by septation, in regular sequence, proceeding out- 

 wardly, till a tissue from sis to eight cells in thickness is formed, 

 the divisions then taking place in irregular order in those cells 

 which form the three or four outermost layers. 



That the cambium is composed of prosenchymatous cell-groups, 

 the combined cells varying in number with the species to which 

 the plant belongs. From the cambium on the phloem side paren- 

 chyma is produced by the rounding-off, and sometimes by the 

 further division of the individual cells, and prosenchyma on the 

 xylem side by the absorption of the transverse septa ; wood-paren- 

 chyma being simply those cambium cell- groups in which such 

 absorption has not taken place. 



That the vessels arise by the fusion of certain cambium cell- 

 groups, which are arranged vertically with regard to each other ; 

 the oblique septa separating the groups being partly absorbed, and 

 the transverse ones entirely so. 



That absorption of the oblique septa appears to commence with 

 the formation of sieve-plates, the pores of which enlarge and 

 coalesce till either there is one large circular aperture through the 

 centre, or the bauds dividing the sieve-plates remain, forming the 

 scalariform septa of some species. 



