27S G. HoaaAN on a new foum of section-cutting machine. 



adapted those three pieces to the machine now before you, upon 

 which she intends to cut sections 6-in. by 4-in. But as I cannot 

 at present enter into a description of them without trespassing upon 

 her privileges, the Society, for the present, must do without them. 

 I now conclude my paper on section cutting, and hope at some 

 future time to describe the best methods and precautions used in 

 hardening tissues to be afterwards cut. The question of hardening, 

 like that of staining and mounting tissues, requires a separate 

 paper for its consideration. 



On the Histology of Plants. 



By R. Braithwaite, M.D., F.L S., &c., 



V. Simple or Homogeneous Tissues. 



{Bead May 22nd, 1874.) 



We may now pass to the consideration of the various tissues which 

 enter into the structure of plants, by which we understand every 

 combination of cells constituting the various organs which con- 

 tribute to the common growth. By examination of the individual 

 parts of which these are built up, we find they may be readily ar- 

 ranged in two groups : — 1. Homogeneous tissues, composed of cells 

 which are uniform or all of one kind, and including Primary 

 parenchyma, Pith, Cortical tissue, Cork tissue, and Cuticle; 2. Hete- 

 rogeneous tissues, in which there is a mixture of different kinds of 

 cells, and embracing the Vascular bundles with their wood and 

 bast parts, the Cambium layer, and the Medullary rays. 



Homogeneous Tissues. 

 1. — Primary or Fundamental Parenchyma is the basis of all 

 new growth, and therefore is found in the young'est parts before 

 the cells have undergone differentiation. As it is constantly 

 increasing by division, it has been named by Continental botanists 

 meristem, and may always be seen in a thin section of the growing 

 point of buds, and in the earliest stage of leaves. Young un- 

 expanded buds of the fig-tree or horse-chestnut afford good 

 examples, and taking sections at various distances from the point, 

 the gradual stages of differentiation may be readily observed. 

 The constituent cells are thin-walled and spheroidal, thus leaving 

 intercellular spaces, and by application of suljDhate of coi^per and 

 liq. potassa^, the cell contents become well defined. 



