Morphology of Vegetable Tissues. By W. H. Gilburt. 805 



example which differs in most important particulars from the con- 

 clusion stated early in this paper. But it must be borne in mind 

 that the development of these xylem elements commenced by the 

 enlargement and division of a single cell, and not simply by the 

 thickening of a cell already existing in the procambium, and that 

 the tissue intervening between the several series of thickened cell- 

 forms, is at first produced from the same layer of cells, viz. those 

 immediately adjoining the pith. This statement is supported by 

 the fact, that, although the bundle as a whole has increased greatly 

 in radial diameter, yet the phloem portion of it remains about the 

 same as at first ; the small amount of apparent growth resulting 

 probably from the greater size of the individual cells, and not from 

 their increased number. We must therefore regard the xylem 

 elements and the cambium, the development of which we have been 

 tracing, as new tissues resulting from the activity of the generating 

 layer of cells, that in the other species produces the cambium at 

 the first. 



The progressive development of the cambium-cells described 

 above appears to hold till the tissue consists of some six or eight 

 cells in thickness, after which division takes place frequently in the 

 cells which form its three or four outermost layers, as I have found 

 thin cell plates between thicker ones, the cells thus cut off being 

 about half the size of those immediately contiguous. 



The species which I have studied, in addition to the three 

 already referred to, are Eihes nigrum, JEsculus hippocastanea, 

 Betulus alba, Quercus robur, Quercus ilex, Acer loseudo-platanus, 

 Fagus sylvatica, Ulmus camfestris, Syringa vulgaris, Castanea 

 sp., Nerium oleander ; and, while I have not been able in all cases 

 to carry back the investigations to the earliest divisions of the 

 generating cells, yet they all agree in this : the cambium tissue is 

 always to be seen next the medulla before the appearance of any 

 thickened cell-forms, and that the farther you can carry the inquiry 

 back, the smaller is the number of cells of which the cambium is 



In one species only, viz. Tilia europiea, have I failed to see the 

 cambium as just described, and that simply from the very sharply 

 curved course taken by the vascular bundles at the apex, and the 

 extreme difficulty of getting a section at all favourable for observa- 

 tion of the earliest stages of development. There is no doubt, 

 however, judging from what I have seen, that it agrees closely with 

 the other species examined. 



Turning now to a consideration of the structure of the cambium- 

 layer, I find that it differs in certain important particulars from what 

 it is generally understood to be. 



In studying this tissue, the plan followed has been to make a 

 series of tangential sections of the region existing between the bast 



