Leaf sheath, near ligule: wheat =oat -barley; rye. 

 Near base : wheat ; rye=barley ; oat. 

 Wheat has the stiffest leaf sheath throughout its 

 length, while rye and oat show the greatest change 

 from base to apes. When all is said however, from the 

 point of view here taken, this feature is of perhaps 

 least value. 



There are similar but not so great differences in the 

 thickness of the cell walls of the epidermis in differ- 

 ent parts of the internode, coupled with the absence, 

 at the base, of stomata and stomatal zones. In all the 

 straws, the thickness of the walls decreases toward 

 the base, their sinuosities are entirely absent, and 

 their caliber becomes much reduced. Indeed, the dif- 

 ferences in the lower part of an internode are so slight 

 as to be practically negligible, although, in unmacer 

 ated epidermis, the oat can be distinguished from the 

 others by the thicker walls. The series are, in order 

 of thickness of ceil wall as follows : 



Lower internode : near top : wheat (9 microns) ; oat 

 (6 microns) = barley = rye. 



Near base: oat (3-6 microns); wheat (2-3 

 microns = barley = rye. 



The width of the epidermal cells of the stomatal 

 zones affords an additional criterion of distinction 

 which is of some help. The following measurements 

 were made on five different leaves and five different 

 stems, the leaf specimens taken near the ligule, and 

 from the internode correspond! ugly near its apex. 

 About 150 measurements of each species were made, 

 each measurement being the total width of from five 

 to twelve cells, taken transversely. Two sets of meas- 

 urements were made several days apart, and they were 

 found to check, this also in the case of the stomatal 

 measurements just beyond. 



Minimum, mean and maximum width of epidermal 

 cells (with wavy outlines) of stomatal zones, (in 



microns) : — 



Leaf sheath Stem 



Barley 16-20-25 15-17-18 



Oat .'. 25-27-31 19-21-23 



Kye 22-24-28 18-20-22 



Wheat 24-27-32 20 - 21.5 - 24 



These measurements may not of course be taken as a 

 single -expression of unvarying size for each kind of 

 straw, but they appear however to express with fair 

 accuracy the relative values of the different kinds. 

 The order of the series for both leaf and stem is there- 

 for: Wheat; oat; rye ; barley, there being less dif- 

 ference for the stem than the leaf. In the former the 

 differences are too slight for practical purposes, and 

 therefor can scarcely be used to advantage. 



Measurements of length of the epidermal cells appear 

 to be of less value that those of width. Wiesner(1900) 

 gives the following dimensions determined by him. 



Length Width 



fmicrons) (microns) 



. Barley 103-224 12-14 



Oat 186-448 12-17 



Rye .. 86-345 12-16 (14) 



Wheat 152-449 18-24 



(14) Hoehnel gives 36-90 as Wiesner's figures (from Wies- 

 ner 1867). In Wiesner 1900 they are given as 12-16, as 

 above quoted. 



Weisner does not tell us what epidermal cells they 

 are that he measured, and it has become quite evident 

 from my own observations that it is important to know 

 this. That bis data are of restricted value appears at 

 once when they are compared with the following made 

 by me on the epidermis which yielded my own meas- 

 urements of cell width, given above. 



Epidermis. — Length of cells in microns. 

 Species Stem (lower internode) Leaf-sheath 



Upper part Lower part 



Barley 39-270 450 30-186 



Oat 45-405 240 225-2100 (15) 



Rye' 30-270 030 45-300 



Wheat 60-300 585 30-330 



(,15) The epidermal cells with straight (non-sinuous) walls 

 are by far the longest, those having lengths of 1,000 to 

 1,500 microns being frequent. 



The length of the cells varies very much with the 

 position, the shortest occurring in the vertical series 

 which include the stomata, the longest in the non- 

 stomatal zones, where the outlines are either less wavy 

 or not at all. In macerations, the latter might easily 

 be overlooked. At all events, with such wide limits, 

 and we note in passing especially the oat, the applica- 

 tion of these measurements would have only an equi- 

 vocal value. 



The stomata show very considerable differences in 

 size when the transverse and longitudinal measure- 

 ments are taken separately. Measurements of 100 to 

 200 stomata taken from five specimens of upper part 

 of leaf and of a lower internode gave the following 

 data. 



Measurements of stomata (in microns). 



Leaf sheath Internode 



Length Width Length Width 



Barley 50 26 47 26 



Oat . . 63 25 55 29 



Rye 56 29 58 31 



Wheat 56 37 56 34 



It has been seen that wheat has by far the widest 

 stomata* while in the leaf sheath the oat has the longest. 

 There is however considerable variation in the size of 

 the stomata, especially from different regions of the 

 organs which carry them. This offers a difficulty of 

 course in view of the fact that in macerations the 

 stomata from these regions are mixed together. The 

 variation due to this alone is indicated in a general 

 way by the following comparative measurements. 



Stomata of internode. 



Basal internode Terminal internode 



(upper end) 



Length Width Length Width 



Barley ....... 45 33 48 33 



Oat 60 45 55 33 



Rye 57 36 60 30 



Wheat ........ 55 45 55 33 



Stomata of leaf sheath. 



New ligule Near base * 



Length Width Length Width 



Barley 43 24 51 19 



Oat 60 27 49 30 



Rye 54 24 62 31 



Wheat 54 35 59 35 



The discrepancies which are apparent in the above 

 tables both for the stomata in similar regions and for 

 different regions teach us that measurements must be 

 used with caution and, beyond a very general purpose 

 of distinguishing between one straw and all the rest, 

 only when a sufficient number of measurements can be 

 made, a caution which applies also to the other meas- 

 urements given above. 



Keys based upon the foregoing characters. 

 A. Epidermal cells with strongly undulating walls, at 

 least toward the sides of the stomatal zones 



leaf-sheath epidermis upper part. 



Walls along the middle of stomatal zones thin 



and straight oat 



Walls of nearly the same thickness and degree 



(*) The width does not include the thickness of the wall 

 of the two adjacent cells. The length is "over all" — that is. 

 includes the total thickness of the end walls. 



