MINUTE STRUCTCRE, 59 



The technical description and terminology of the various tissues 

 of plants must be sought for in text books devoted to the subject ; * 

 we can only here offer so much explanation as will render the 

 illustrations intelligible to the general reader. 



All complete vegetable structures consist of cells for the most jiart 

 indistinguishable by the naked eye. Each living evil in what is 

 conveniently regarded as its normal state at the epoch of commencement 

 of growth consists of (1) a transparent colourless membrane called the 

 cell-wall which encloses (2) the protoplasm, "the physical basis of life" 

 as it has been aptly termed by Professor Huxley, which forms a layer 

 closely lining the cell-wall, (3) a denser rounded mass of the protoplasm 

 called the nucleus, which is eitlier embedded in the layer of protoplasm 

 lining the cell wall, or is suspended in the middle of the cell by fine 

 threads of protoplasm, the intervening space (4), the vacuole, being 

 filled with a colourless fluid, the cell-sap. Cells so constructed are more 

 or less of spherical form and may be seen in the young shoots of all 

 plants, in some of which they are found more favourable for observation 

 than in others, as in the pith of a young growing slioot of the elder, 

 the hairs on the stamens of Tradescantia, etc. : but in most cases a 

 high magnifying power is necessary for the several parts above described 

 to be clearly made out, though in the footstalk of a rliubarb leaf they 

 are so large as to be readily seen by the naked eye. Such it is usual 

 to regard as the fundamental form of vegetable structure, from which 

 all subsequent developments originate. In all the most highly organised 

 plants, although the cells have an indepemlent existence for a time, 

 there are always a large number of them in close contact and tirndy 

 united, forming a cellular tissue, a number which increases as groA\th 

 progresses till in the full-grown plant, even when of only moderate 

 dimensions, the number of cells in the aggregate exceeds the power of 

 ordinary calculation. Nevertheless, even in the higher plants isolated 

 cells occur during temporary states of existence as ])ollen grains, fern 

 spoi'cs, the antherozoids of mosses, etc. The actual forms ami sizes 

 of the cells are as varied as the structures of which they form the 

 constituent parts ; they are subject to regular changes like the whole 

 plant which they build uj). Only those cells arc in a living state 

 which contain protoplasm ; they alone can grow and give rise to new 

 cells ; cells devoid of protoplasm may, however, be of service to the 

 plant as supports and protection to the growing parts, or as conduits 

 and store places. 



Every new growth begins with a change in the protoplasm by virtue 



* Among the best are Sachs' Lehrbuch der Bolanik, English translation by Dr. Sydney H. 

 Vines ; the latter author's recently published Sludznt's Text Book of Botanij ; and De Havy's 

 Comparative Anatomy of the Vegetative Orfjans of Phanerogams and Ferns, translated bj' 

 F. 0. Bower and Dr. H. Scott. 



