712 MICKOSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS 



Canada balsam, and are then very showy specimens for the gas- 

 microscope. The number of beautiful and interesting objects which 

 may be thus obtained from even the commonest trees, shrubs, and 

 herbaceous plants at the cost of a very small amount of trouble 

 can scarcely be conceived save by those who have specially attended 

 to these wonderful structures ; and a careful study of sections 

 made in different parts of the stem, especially in the neighbourhood 

 of the 'growing point,' will reveal to the eye of the physiologist 

 some of the most important phenomena of vegetation. The judi- 

 cious use of the staining process not only improves the appearance of 

 such sections, but adds greatly to their scientific value. Fossil 

 woods, when well preserved, are generally silici/ied, and can only 

 be cut and polished by a lapidary's wheel. Should the microscopist 

 be fortunate enough to meet with a portion of a calcified stem in 

 which the organic structure is preserved, he should proceed with it 



FIG. 556. Epiderm of leaf of 

 Yucca, showing stomates. 



FIG. 557. Epiderm of leaf of Indian 

 corn (Zea Mais), showing stomates. 



after the manner of other hard substances -which need to be reduced 

 by grinding. 



Epiderm of Leaves. On all the softer parts of the higher plants, 

 save such as grow under water, we find a surface layer differing in 

 its texture from the parenchyme beneath, and constituting a dis- 

 tinct membrane, known as the epiderm. This membrane is composed 

 of cells, the walls of which are flattened above and below, whilst 

 they adhere closely to each other laterally, so as to form a continuous 

 stratum (figs. 560, 562, a, a). The shape of these cells is different in 

 almost every tribe of plants ; thus in the epiderm of the Yucca (fig. 

 556), Indian corn (fig. 557), Iris (fig. 561), and most other mono- 

 cotyledons, they are elongated, and present an approach to a 

 rectangular contour, their margins being straight in the Yucca 

 and Iris, but minutely sinuous or crenated in the Indian corn. 

 In most dicotyledons, on the other hand, the cells of the epiderm 

 depart less from the rounded form, but their margins usually 

 exhibit large irregular sinuosities, so that they seem to fit together 



