compressed longitudinally (figure 14), and the stomata 

 well developed. Indeed so much difference is there 

 that it is difficult to recognize that one is dealing with 

 the same stem. It will be readily understood that it 

 becomes much more difficult to distinguish between dif- 

 ferent kinds of straws if only the epidermis from the 

 lower portions of the internodes is regarded. Sucli 

 characters as may enable one to make these and similar 

 distinctions are found only in the upper part of the in- 

 ternodes. 



Epidermis of the leaf (figures 10-13). In straw, in 

 the ordinary commercial sense, the leaf blades are pre- 

 sent in such small quantities as to be negligible. They 

 are broken off in threshing and become as chaff. The 

 leaf sheaths however are practically always adherent 

 and form part and parcel of the straw and constitute a 



cw- 



Fig. 14. — Diagrams of the dwarf cells and of an epidermal 

 cell (wheat), a, dwarf cells, en face; b, lateral view; cut, 

 cuticle; c, epidermal cell in perspective; d, dwarf cells of 

 barley. 



not inconsiderable proportion of straw paper pulp. The 

 epidermis is moreover more evenly and fully developed 

 throughout the whole length of the leaf -sheath. The 

 longitudinal walls of the longer cells of the outer sur- 

 face are thicker and usually strongly undulating, the 

 dwarf cells may be developed into short protruding 

 hair (wheat) and are generally in twos (figures 9 and 

 13). The epidermis of the thin leaf margins and of the 

 inner surface of the leaf-sheath is very thin, as are the 

 walls of the cells. They are here also without undula- 

 tions, and dwarf cells are relatively few. The relative 

 amount of epidermis from the leaf-sheath as compared 

 with that of the stem, together with its uniform char- 

 acter makes it an important means for the identification 

 of the kind of straw, especiallv in the form of pulp. 

 THE INTERNAL TISSUES. 

 The epidermis encloses a variety of tissues and a still 

 greater variety of their component cells. The latter 

 may be segregated into two groups, according to their 

 dimensions; roughly, those which are rather short 



(parenchyma) and those which are elongated (prosen- 

 chyma). These distinctions are made chiefly for the 

 purposes of description, and are used as such. It has 

 been pointed out that the epidermis is differentiated 

 into longitudinal zones ("fluting") which are readily 

 distinguishable by the character of the cells composing 

 them, and most easily by the' presence or absence of 

 stomata (figures 6-13). Those with stomata may be 

 called the stomatal-zones for convenience. These dis- 

 tinctions hold for both leaf and stem and with them in 

 mind we may proceed to consider the arrangement of 

 the internal tissues of both. 



Internal Tissues of the Stem. 



The Chlorenchyma.— Lying just beneath the pore 

 zones of the epidermis are to be found corresponding 

 zones of very thin walled and loosely arranged cells 

 which during the life of the plant contain green color- 

 ing matter (chlorophyll) (figure 4, ch.). These cells 

 constitute the chlorenchyma which appears merely as 

 green color to the eye, arranged in longitudinal zones. 

 The chlorenchyma is the active seat of starch forma- 

 tion, for which purpose carbon dioxide is necessary. 

 This finds its way by diffusion into the chlorenchyma 

 through the stomata pores. This relation explains the 

 distribution of these pores in longitudinal zones. 



The chlorenchyma is best developed in the exposed 

 upper part of the internodes, especially of the topmost 

 slender internode which bears the grain (figure 4). 

 As one descends an internode, the chlorenchyma be- 

 comes less and less conspicuous, until near the base it 

 may not be present at all (figures 2 and 3). It has been 

 noted above that there are here very few stomata, cor- 

 responding with the absence of chlorenchyma. 



The "fluting" can sometimes be seen e.g. in wheat, 

 by the naked eye to occur roughly in pairs. This is 



Figuresl5. — Diagram of a stoma seen in transverse sec- 

 tion, barley. 



brought out clearly in a transverse section (figure 4). 

 in which it is seen that the chlorenchyma strips are 

 paired with reference to certain groups of cells (vas- 

 cular bundles). Sometimes the neighboring strips of 

 adjacent pairs run together, making a group of three; 

 in other instances the spaces between the pairs are 

 equal to the spaces between the members of a pair, so 

 that the fluting is less obviously regular, but more so 

 in some straws e.g., wheat, than in others. 



The chlorenchyma" in the lower internodes is more 

 tangenfially compressed than in the uppermost, 1 is re- 

 latively shallower and is more irregularly disposed. 

 The topography as revealed in transverse sections is 

 fairly characteristic for each of the grains (figures 

 16-19). 



The Zone of Fibres (bast).— The longitudinal zones 

 of epidermis devoid of stomatal pores are on the other 

 hand underlain by a mechanical tissue composed of 

 much elongated cells (fibres). To each zone, and lying 

 just below the fibres, is a vascular bundle (figure 4). 

 According to the age of the stem and to the vertical 

 position, the extent of fibrous tissue varies, it being re- 

 latively greatest in the lowermost part of the internode, 

 and bears an inverse relation to the chlorenchyma 



