32 The Mode of Examining the [*'SoZ^u/janTi^m' 



ferous vessels and Kesin canals are best considered by themselves. 

 Again, the whole of the external or Limitary Tissues of plants can best 

 be considered as forming a great group, including Cuticle, Epidermis, 

 Hairs, Scales, Cork, Subepidermal tissue, &c. The group of tissues 

 found in the Fibro-vascular bundles of plants can also be advan- 

 tageously studied as a whole. In the Arrangement of the Tissues 

 we shall foUow, to a certain extent, Sachs,* as he enters very fully 

 into the subject. We shall first consider Cells and Cellular tissue ; 

 then the Limitary tissues of j)lants, including Cuticle, Epidermis, 

 Hairs, &c., the Fibro-vascular bundles, and, lastly, the Laticiferous 

 tissues and glands. If we begin by examining a young root, such 

 as that of the white mustard, we can at once see the relationships 

 of the various groups of tissues. If we take a transverse section of 

 a young root, and place it under the microscope, we see three 

 separate tissues. Externally, we have the Limitary tissues, con- 

 sisting of small epidermal cells, giving rise to numerous fine hairs. 

 Within the limitary tissues we have a great mass of cellular tissue, and 

 in the centre we have the fibro-vascular bundle more or less developed. 

 In many plants we have the Laticiferous tissues developed, but they 

 are in general altered portions of one or other of the tissues, and 

 not a separate group ; but as they are easily distinguished physio- 

 logically, it is perhaps best to keep them separate. If we examine 

 the growing part of the root, we find that the tissue presents a 

 uniform appearance, all the cells being similar, and it is only as 

 growth goes on that the cells become variously modified to sub- 

 serve various physiological purposes. Some of the cells became 

 modified to form a protecting covering ; others to give support to 

 the softer parts, to form a skeleton, or a series of conducting tubes 

 for the conveyance of the sap and juices of the plant, while others 

 may contain stores of nutriment for the future use of the organism. 

 I. The Cell. — If we examine the cells of the growing point of 

 a root, as seen, for example, in a longitudinal section of the young 

 root of the white mustard, after tinting with carmine solution, 

 we see a number of small cells, consisting of a very delicate cell- 

 wall, containing a mass of granular protoj^lasm, and a very large 

 brightly-stained nucleus. In the youngest stage the cell thus 

 consists of three parts : — 1st. A very delicate cell-wall ; 2nd. A mass 

 of granular protoplasm; and 3rd. A very large central nucleus. 

 If we examine the cells at a short distance from the growing part 

 of the root, we find that the cell-wall has enlarged, in general 

 growing more in length than in breadth, but consisting of the same 

 parts as those at the apex. Further away still we find that drops 

 of fluid are forming in the protoplasm ; that the cell-wall is no 

 longer filled up by the protoplasm and nucleus alone, but there 

 are also drops of cell-sap beginning to form. If the cell in this 

 * ' Lehrbiicli cler Botanik.' Engelmann. Lcii)zig, 1 SG8. 



