NUMBER OF STOMATA IN PHASEOLUS VULGARIS STUDIED WITH THE ANALYSIS OF VARIANCE TECHNIQUE

Abstract

THERE IS great variation in number of stomata as reported by Zalenski (1902), Yapp (1912), Loftfield (1921), Rea (1921), and Salisbury (1927) between parts of the same leaf and between leaves of the same plant. The analysis of variance method (Fisher, 1936) is well adapted for gaining a comprehensive view of such variation. This method is illustrated in some detail by Snedecor (1934) and tables for determining F and P are presented by Trelor (1935). A conception of the variation in number of stomata per unit area of leaf surface as determined by this method should aid materially in appraising the role of stomata in controlling transpiration. There is a difference of opinion as to whether stomata have a controlling influence upon transpiration. Maximov (1999) and MIiller (1931) present reviews of the literature dealing with this question. It is noticed that usually comparisons are made between species. Instead it would seein preferable to compare vaTieties or selections within the same species, for, as stated by Miller (1931), it should not be overlooked that different species possess structural differences other than number of stomata which may greatly influence transpirational rate. In this connection data by Muenscher (1915) are of interest. His data show a difference in transpiration rates between two selections of Pelargoniuzm zonale differing in stoma number; the selection which has the more stomata has also the higher rate 'of transpiration. Experiments designed to discover a difference in transpiration rate associated definitely with a difference in some particular leaf character and to discover if there is a correlation between transpiration rate and leaf characters in the segregates of a cross between the two selections are of interest. After an extended search to obtain material for such an experiment, two selections in Phaseolus vulgaris L. which differed significantly from each other in stoma number were located. These two selections are designated selection 5 and selection 7, respectively. Various methods of preserving and staining leaves in toto were tried. A procedure that proved satisfactory was to kill, preserve, dehydrate, and stain simultaneously in a mixture of 1 gram of methylene blue in 500 cc. of 95 per cent alcohol. The material could remain indefinitely in the fluid without overstaining. Observations were made by using a 1oX objective and a 25X eyepiece. The size of the field of vision was reduced, as the occasion demanded, by placing on the eyepiece diaphragm a metal disk having in its center a hole of convenient size. It wa.s desirable to use a field of vision as small as practicable to facilitate counting and also to avoid veins.