806 Transactions of the Society. 



fibres and the true wood, keeping each section separate and 

 numbered in its proper order. 



Now, the only statement made, concerning the structure of the 

 cambium, is, that its cells are thin-walled, close-fitting, filled with 

 protoplasm, and generally prosenchymatous in form. 



In this part of my investigations, serial preparations of the fol- 

 lowing species have been made : — 



Fraxinus excelsior . . . . 2, 3 I Larix eiiropa^us 8-10 



Prunus lusitanicus .. .. 4-6 i Taxus baccata 6-8 



Tilia europsea 4 | Ficus carica 4 



Syringa vulgaris 3, 4 [ Cy tisus laburnum . . . . 2 



Acer pseudo-platanus . . .. 4 Corylus avellana 6-8 



Sambucus nigra 2, 3 i Salix sp 6-8 



Cratsegus oxyacantha . . 4,5 j Eucalyptus sp 4 



Ilex aquifolia 8, ?* i Juniperus communis . . . . 8 



Cornel sp 4 i Wellingtouia gigantea . . ?' 



Ailantlius glandulosus . . 4 ' Ceclrus sp ?* 



Salisburia adiantifolia .. 12,13 i 



In all of them I find the cambium composed not of prosenchy- 

 matous cells, but of prosenchymatous cell-groups, i. e. of cells so 

 grouped, that the terminal ones of each group being more or less 

 pointed at one end, the group is, as a whole, more or less prosen- 

 chymatous in form. 



The number of cells so grouped varies with the species, and also 

 in some species it varies within certain narrow limits. It may, 

 however, be taken as true, that the longer the prosenchymatous 

 elements of the mature wood are, the greater the number of cells 

 composing the cambium cell-groups will be. Thus the figures 

 placed to each name in the foregoing list of species, indicate the 

 number of cells grouped together in the cambium ; and it will be 

 seen that in the Conifers, which possess the longest prosenchy- 

 matous wood-cells, there are from six to eight in Taxus, and twelve 

 to thirteen in Sahsbui'ia ; while in Cytisus, which has the shortest 

 wood-elements I have seen, there are but two.f 



That this is the true character of the cambium is proved from 



* In these species, owing to the line of section being somewhat oblique to the 

 course of the tissue, the numbers could not be counted satisfactorily, as frequently, 

 owing to the comparatively great length of the group, the whole of it was not pre- 

 sent. 



t Each member of these groups is a complete cell, 1. e. possesses a distinct 

 nucleus, in which one or more nucleoli are to be seen. After the absorption of 

 the transverse septa referred to in the next paragraph, the nuclei approach each 

 other, and are frequently to be seen in a group near the centre of the young wood- 

 cell. Coalescence of the nuclei appears now to take place. In Laburnum I have 

 seen, first, a nucleus in each cell ; after absorption, two nuclei partly overlying 

 eacli other ; and in wood-cells in winch thickening is taking place, only one 

 nucleus about twice the size of the original ones. The same remarks apply to one 

 or two other species examined in this regard. In Salisburia fusion of the nuclei 

 takes place undoubtedly so far as reducing the original number to half, while in 

 size they are double. These remarks are founded on observations made on tissues 

 in a state of rest, and since the date of the paper. 



