84 



CELLULAR TISSUE. 



to touch. The rods may be as high as the epidermal cells (Strelitzia, Internodes of 

 Saccharum, &c.) or in most cases much higher, — the longest, especially those observed 

 on the nodes of Saccharum, attain a height of more than loo/t and 150/^. Their 

 height is however very unequal. Their thickness reaches usually on the average about 

 i/i, but in the largest often three or four times as much. Their form is cylindrical, 

 or, in the case of the thickest, more or less angular or compressed like a riband. 

 They are straight in their lower part, which is attached to the epidermis, but the 

 upper ends are, in the shorter ones, hooked, in the longer ones very strongly curved 

 like a crosier, or a cork-screw curl. Their substance is homogeneous, or, when 

 they are large, longitudinally striated. To the naked eye the rod-like coverings 

 appear as a w'hite mealy covering of the surface varying in mass according to 

 the size and number of the rods, and easily scraped or brushed oflf. It is most 



SpgqpppqgQ^ppropc 



Fig. 28.— Transverse sections througli tlie stem of Saccharum officinarum. ^ (375) surface of a mature young internode, 



£ (142) of a similar node. 



obvious on the leaves of the Heliconia above cited, and on the nodes of Sac- 

 charum. 



That form of the covering is termed a simple granular layer in which granules 

 of wax are superposed on the cuticle, side by side in a simple layer, and not heaped 

 upon one another. The granules have on the average a size up to i/i : they are 

 spherical, or in the form of very short rods perpendicular to the surface (e. g. Allium 

 fistulosum, branches of Acer striatum), and form, when of the latter shape, the 

 transition to the rod-like coverings. They lie either at wide distances apart (e. g. 

 upper surface of the leaf of Tropseolum majus, Begonia semperflorens and 

 other spec, Vitis vinifera), or they approach one another leaving small spaces, or 

 till they touch one another, the latter, e. g. in the mature leaves of Tulipa, Echeveria 

 pumila, and other species, Dianthus caryophyllus, the red and white cabbage, &c. 

 When the granules are not too far distant from one another they form the white 

 or blue, easily removed bloom, to which so many so-called glaucous parts owe their 

 character. Of the innumerable examples of this besides those already cited may be 

 named the parts of the epidermis of the above-cited grasses, which do not bear 

 rods, the leaves of Iris germanica, pallida, Galanthus nivalis. Allium, Brassica 

 oleracea var., Mesembryanthemum spec, Calandrinia speciosa, the upper part of 

 the inner side of the leaf-pitcher of Nepenthes (Wunschmann, /. <r.). 



A large number of glaucous and hoary parts of plants from the most various 

 families are covered with the wax-bloom of the fourth type, which is termed an 



