shows part of a seventh internode. The thickness of 

 the various straws bears no relation to the stature. 



A conspicuous feature of the grass stem and leaf al- 

 ready referred to is the fine longitudinal ribbing and 

 alternate "fluting", especially obvious in straw which 

 still shows the green color, though it can be seen quite 

 readily by the deep yellow color after the green has 

 faded away. This appearance is due partly to the pre- 

 sence of low longitudinal ridges, and partly to the 

 structure underlying the outer tissue, the epidermis. 

 This relation will be made clear later. 

 Anatomical Structure. 



A glance through the microscope at a bit of straw, 

 however prepared, will show at once that the mass is 

 made up of a large number of small units, each com- 

 posed of a wall enclosing a space which may be either 

 empty or contain the remnants of various substances 

 which were important during the life of the plant. It 

 is convenient to designate these units by the term cells, 

 as originally used. (4) 



Structural groupings of cells of similar size and shape 

 are called tissues. In the immediately following para- 

 graphs the form and dispositions of the cells and tis- 

 ues will be described. It will be convenient to begin 

 by examining the structure of a stem as seen in trans- 

 verse sections. 



(4) "Cell" was used by Robert Hooke in 1665 for the 

 cavities seen in cork. The term has now a more funda- 

 mental significance, being applied to the living matter 

 which, in plants, builds up a cellulose skeleton by which 

 the form of the plant is maintained. There is no living 

 matter present in "straw", which is merely the rela- 

 tively indestructible skeleton of the erstwhile live plant. 



THE STEM. 

 If such a section is taken just above the node, where 

 the stem is not hollow, the following structure will be 

 seen (figure 2). 



The section is nearly circular, and appears made up 

 of a mass of round cells constituting the parenchyma, 

 the largest in the middle, and grading in size toward the 

 edge when they meet with a much denser lot of tissues. 

 These are evidently arranged in groups of cells (the 

 fibro-vascular bundles) of different sizes, between 

 which the parenchyma extends toward the periphery 

 of the section. There are apparently two, but strictly 

 speaking more than two, circular series of fibro-vas- 

 cular bundles, the inner of larger ones, and an outer of 

 smaller ones, paced quite close to the surface of the 

 stem. Between the bundles of the outer series the cells 

 are very small, and as will be seen, make up a layer of 

 fibers (bast), (c/.) figure 5). 



Bounding the whole is a single layer of cells of small 

 size and approximately quadrangular in transverse sec- 

 tion constituting the epidermis. On comparing with a 

 section (figure 3) from a somewhat higher level in the 

 internode where the stem is hollow and where the tissue 

 arrangement is best displayed, it will be seen that here 

 the structure differs from that just at or above the node 

 chiefly in the circumstance that the parenchyma in the 

 middle has broken clown thus leaving the space (fis- 

 tula). At a still higher level ii is seen that there may 

 be an interruption of the dense mass of small-celled 

 tissue just beneath the epidermis, by stretches, occupied 

 by very thin walled and loosely arranged cells (the 

 chlorenchyma) which, when the plant is alive, contain 

 the green coloring matter (figure 4). 



If now a section running lengthwise the stem is 



/■~;s""<f ; '' .": 7 " ' ' Tit 



' ■ ■ 



•'■■ 



■' MS. 



%& 



;.. .'■ ; ■' 



Figures 6-9. — The epidermis viewed en face of the stem (upper part of a lower internode) of barley, oat, rye and 



wheat resp. X 174. 



