28 ON GROWTH AND EXTENSION IN THE VEGETABLE KINGDOM. 



hypothesis, a single glance with a microscope is enough to show 

 that the skin, tlie veins, and the muscles, at least in their perfect 

 state, have an uniform, and for the most part fibrous, texture; 

 whilst, on the contrary, plants in their youth as in old age clearly 

 show their cellular structure. 



In order, therefore, to judge of the mode of growth of plants, 

 we must in the first instance direct our attention to the growth 

 and increase of their cells. It will be most convenient to select 

 for that purpose those plants and those parts which increase the 

 most rapidly, as in them the differences are the easiest to observe. 

 We have made use of an easy and simple method, the placing 

 bulbous roots over glasses full of water, where they, under proper 

 treatment, rapidly put forth roots, which soon attain a consider- 

 able length, whilst at the same time, though with less rapidity, " 

 they shoot out from above their leaves and stalk. 



Among a number of experiments of this kind I will refer to 

 one in particular. After the fibrous roots of a hyacinth had 

 attained tiie length of about an inch, they were marked with 

 cross lines of Prussian blue, as this colour holds much the best 

 in water, and does not injure the tender roots. After some days 

 the fibres Jiad attained a lengtli of 3 inches ; and it was clearly 

 shown tliat vthe portion next the bulb, for a length of about 10 

 lines, had not lengthened at all ; that the ball-shaped, readily 

 distinguishable aptx of the root, about 1 line long, had also 

 remained without lengthening, and thus that the whole increase 

 liad taken place in the portion of the root, about 2 lines long, 

 between the base and the apex. 



We may now consider the changes which the cells have under- 

 gone during the increase, and for that purpose examine them 

 under a magnifying power of 315 diameters. Tlie upper un- 

 lengthened portion consists of cells (parenchyma-cells) connected 

 • together by their ends, and all shrunk or contracted in length. 

 The adjoinhig portion consists in the uj)per part of short cells, 

 which are already lengthened in the lower part. Tliis is most 

 striking in the upper unlengthened portion. It diminishes again, 

 and the lowest cells are similar to those of the root-point. We 

 here speak of the outer cells of the root only : the inner ones are 

 of the same length, only broader. In the centre of the root may 

 be seen the long, narrow cells which are continued from the basis 

 of the root to the commencement of the root-point, but never 

 penetrate into the latter, thus pointing out the root-point as a 

 distinct substantive organ. Amongst these long, narrow cells 

 in the centre of the fibre are placed the spiral vessels, which, 

 however, cease at a considerable distance from tiie root-point. 



The lengthening of the fibres, or rather their growth, com- 

 mences therefore with the lengtliening of the cells. But tliis 



