60 GENERAL REVIEW OF THE ORCHIDEA\ 



of tlie vital force with which it is endowed, a power that can no more 

 be accounted for or explained than the states of consciousness that | 

 enables us to distinguish a sound from an odour, a colour from a | 

 flavour, or any other ultimate fact of Nature. There is a continuous , 

 movement of the particles, and although extremely slow and imperceptible 

 to our limited powers of vision, such a movement is inseparable from , 

 the idea of life. This movement results, in all the higher forms of 

 vegetation, in a division of the mother cell into two others more , 

 or less like itself, and these again divide in like manner. As division 

 and sub-division ])roceed, a differentiation also takes place in the cell : 

 contents ; chlorophyll granules are formed in some, starch-grains, resin, 

 crystals of various kinds, etc., occur in others ; as well as a modification 

 in form according as each fulfils its own definite part in the economy 

 of the plant. 



The numerous and densely crowded cells form the " fundamental tissue " ■ 

 from which in course of time, and in accordance with varying require- 

 ments, different layers of tissue develop differently, so that the adult 

 plant consists of differentiated tissues. In general, the whole mass 

 of tissue is definitely bounded on the outside by an Epidermal layer ' 

 or outer skin consisting of one layer of cells. This surrounds and 

 encloses a rind or "cortex" of several layers, whilst the centre is 

 occupied by a mass r)f cells, some of Avhich remain unchanged while 

 others are gradually converted into long strands. These strings of tissue, 

 the fihro-vasnday bundles, usually follow in their longitudinal course 

 the direction of the most vigorous groM'tli which immediately precedes i 

 their differentiation. Xot only the cortical layers, but also the vascular i 

 bundles and the fundamental tissues are more less differentiated, the 

 sub-epidermal into layers of a different nature ; the bundles also exhibit 

 differentiation, and generally in a still higher degree. In this manner 

 arise in the higher plants Sysfernx of Tismes. ^ 



In two or more years' old stems of the Dicotyledonous division of ] 

 flowering plants, also of the Gymnospermous Orders (Conifers, Cycads, ' 

 etc.), the cnmponent tissues are arranged in concentric rings as is 

 shown in the wood of our common trees and shrubs which consists 

 chiefly of fibro-vasculai' bundles so strongly developed by the continuous ] 

 formation of tissues of which they are composed, that they finally almost 

 replace the intermediate fundamental tissue ; in the leaves, the fibro- 

 vascular bundles (veins) are netted (reticulated) or otherwise more or . 

 less irregularly disposed. On the other hand, in the Monocotyledonous 

 Division, that to which the Ouchide.e belong, the fibro-vascular bundles ; 

 of more than one year's old stems as in Vanda, Cattleya, Dendrobium, ; 

 etc., and also in the pseudo-bulbous species, are isolated and separated i 

 from each other by fundamental tissue ; and in the leaves they ai'e I 

 either parallel to each other or symmetrically placed on each side of | 

 the midrib. 



