Notes on Some Grasses. IX. Systematic Significance of Bicellular Microhairs of Leaf Epidermis

The bicellular microhairs on the leaf epidermis of grasses were re-examined from a systematic point of view. The following four relationships were analyzed to establish characteristics of the hair: (i) ratio of total length to maximal width, (ii) ratio of length of upper cell to that of lower cell, (iii) angle between axis of the hair and shortest line connecting basal rim with rim of maximal width, and (iv) difference in thickness of cell membranes between upper and lower cells. Within (i), (ii), and (iii), five classes were established to show the various ratios or angles. The classes with smaller values were referred to the panicoid hairs and those with larger ones to the chloridoid hairs (tables 1, 2, 3). The total of the values was denoted as "index value." 2. In total, 238 species were observed representing four subfamilies (table 4). They can be divided into two groups: species having low (1-5) and those having high (6-10) index values. In the former, the cell membranes of the upper cell are mostly thinner than those of the lower cell, while in the latter the cell membranes of the upper and lower cells are generally similar. These two groups represented by different index values correspond to the two types, panicoid and chloridoid, established by Prat (7). 3. Panicoideae and Eragrostoideae were compared as to their microhairs. Different tendencies between the two subfamilies were confirmed in all the four characteristics. The hair characters and the systematic grouping are correlated: chloridoid with Eragrostoideae, and panicoid with the other subfamilies. Several species represent cases contradicting the correlation, however, most conspicuously, some species of Eragrostis on one hand and Ischaemum on the other. 4. Several genera show wide variation in characteristics of microhairs which may be useful for their taxonomy. 5. The microhairs of Bambuseae seem to be unique, showing nearly equal basal and maximal width throughout the species observed, although they are similar in shape to the rod-shaped microhairs of other species.