156 PROGRESS OF MICROSCOPICAL SCIENCE. 



to lose itself in a capillary network. 2. The vein begins either in 

 the point of the villus (rabbit, man) or near to the same (rat), and 

 generally goes directly into the submucous tissues without receiving 

 any lateral branches ; or it rises near the base of the villus and re- 

 ceives more or less numerous lateral branches from the glandular layer 

 (dog, cat, pig, hedgehog). 3. In none of the animals examined was 

 there to be found the often cited arrangement of an arterial stem 

 going to the point of the villus, and of a descending venous stem with 

 a simple connecting cajjillary network between both stems. This is 

 of importance with regard to the erection of the villus. 



Microscopic Structure of the Cortical and Corky Tissue of Plants. — 

 Dr. Braithwaite, F.L.S., is now publishing, in the ' Journal of the 

 Quekett Club,' a series of lectures on vegetable histology, which are 

 of great interest. From a proof sheet of the last number of that 

 Journal which he has sent to us, we abstract the following account of 

 the structui-e of cortical tissue and cork, which are two of the group 

 of homogeneous or purely cellular tissues. He says of the first, that 

 it includes that portion of the stem lying between the fibro-vascular 

 bundles and the epidermis or coi-k, and in leaves between the cuticle 

 and vascular bimdles of the nerves ; it is therefore most distinct in 

 parts exposed to the air and light. The primary bark proceeds directly 

 from the primordial tissue of the growing point, and rapidly increases 

 by cell division. In annual plants it is completed simply by extension 

 of these cells, as it is also in perennial plants which cast off their bark 

 by cork tissue arising under it ; but in those like the holly and the 

 mistletoe, which do not do so, certain portions of the cortical tissue, 

 by mother cells, continue to reproduce new tissue of the same kind. 



Cortical tissue consists entirely of parenchym cells, which in leaves 

 usually remain with thin walls, but in the stem are variously modified 

 and may be divided into an inner and outer rind. 



The inner rind is formed of layers of thin-walled spheroidal cells, 

 with their surfaces only slightly in contact, and thus interrupted by 

 apertures of various sizes. Lignification of the cellulose case very 

 rarely occurs, but in a few instances grouj)S of strongly thickened cells 

 are seen, distinguishable by their size and colourless contents ; the 

 ash, beech, labm-num, and Hoya afford examj)les. The contents of the 

 cells of this layer are starch, with the addition of chlorophyll in the more 

 external, and in some instances crystals are also present. Again in 

 inilky-juiced plants bast vessels occur, which are connected with similar 

 vessels of the bast bundle, and single and grouped bast cells are seen 

 in the inner cortical layer of the leaf-stalk of cycads and the bark of 

 many palms. Within this layer also occur the resin, oil, and gum 

 canals peculiar to many plants. 



Tlie outer rind, Collenchyma. — The outer layer consists of rounded 

 parenchyma cells with little or no thickening, but often more or less 

 elongated, or the cells have all irregular strong thickening of their 

 walls or angles, and then constitute collenchyma. When the outer layer 

 of this sub-epidermal tissue consists of thin-walled parenchyma and 

 collenchym cells, the latter are in grouj)S overlying the bast jiart of 

 the vascular bundle, while the thin-walled cells reach the ei^idermis, 



