III. THE TECHNIQUE OF AUXIN DETERMINATIONS. 21 A. Morphology of the Avena Seedling 21 B. Evolution of the Avena Test Method 24 C. The Avena ISIethod in Its Present Form 27 1. Dark Room and Equipment 2. Preparation of Test Plants 3. Preparation of the Agar 4. Technical Modifications 5. Evaluation of Results 6. Positive Curvatures 7. The Maximum Angle 8. Variability of the Test D. Other Methods of Auxin Determination 1. Straight Growth 51 2. The Pea Test 3. Epinastic Responses 4. Other Methods IV. FORMATION AND OCCURRENCE OF AUXINS. .

to the question of the validity of our postulates regarding the equivalence of the physical boundary conditions to the s.p.b.c. and the existence and range of the interval G. These points must be investigated separately for each individual case, using primarily the standard methods for the study of the behavior of solutions of a differential equation in the neighborhood of a singular point.The writer is greatly indebted to his colleague, Prof. Marston Morse, for numerous suggestions and much helpful discussion in connection with the proof that the eigenvalues of X are minima of Q/N for suitably restricted classes of admissible comparison functions.

The senescence of oat leaves has been studied by following the loss of chlorophyll and protein and the increase of a-amino nitrogen, after detachment and darkening. Protein Senescence has long been regarded as an essentially degradative process, and the rapid onset of proteolysis in isolated and darkened leaves has been documented since 1930 (3,28,29 found, inter alia, that the amino acid L-serine enhances senescence, thus acting in the opposite direction to cytokinin (22, 26). In explanation it was suggested that the serine might become incorporated into the active center of one or more proteolytic enzymes participating in the senescence process.The present investigation was therefore undertaken, firstly, to find out more in general about the progress of senescence in the oat leaf, and about the antagonism between L-serine and kinetin; secondly, and more specifically, to see whether there was evidence that proteolytic enzymes are, in fact, synthesized in the senescing leaf, and if their amount increases with time.A preliminary account of some of the results has been presented earlier (12).MATERIALS AND METHODS General Procedure. Oats (cv. "Victory") obtained from the U. S. Department of Agriculture were husked, soaked, and planted in vermiculite. They were grown 50 cm below a bank of eight 20-w cool white fluorescent lights giving 6.4 X 10-2 watts/cm2 at about 23 to 25 C for 7 days. The first leaves, which were then about 12 cm long, were cut off and the apical 3 cm placed on slides over moist filter paper in Petri dishes, a minor modification from the procedure previously used (25, 26), which in turn was based on work of Gunning and Barkley (6). Usually a single 10 ,ud drop was placed in the center of each leaf, as was previously done for the kinetin bioassay (25). This drop contained the test substance together with Mcllwain buffer, pH 4.7, diluted 1: 10, and 0.2% Tween 80. The isolated leaves were left for 72 hr (or occasionally for 96 hr) in darkness, at which time about 50% of the chlorophyll had disappeared. The chlorophyll and a-amino nitrogen of groups of five leaves were then extracted into boiling 80% alcohol for 30 min, the solution was made to 10 ml, its absorbance at 665 nm was read for the chlorophyll content, and an aliquot was taken for determination of a-amino nitrogen by the Moore and Stein method (16). The extracted leaves were then washed twice with 80% alcohol, the protein was solubilized with I N NaOH and determined by Miller's (14) modification of the Lowry et al. method (9). Initial values of chlorophyll, a-amino nitrogen, and protein were determined on a leaf sample at the beginning of each experiment, and the results below are expressed as a percentage of these initial values.Analyses of variance were carried out on each experiment except the time course (Fig. 1)

The paper deals with the general problem of the physiological basis of branching, and the roles of known and unexplored factors in sensitivity to apical dominance. It is shown that when pea seedling shoots are completely or partially inhibited by other shoots on the same plant auxin can promote their elongation, even though it does not have this effect on inhibited buds. This influence of auxin is only exerted on internodal elongation and not on apical growth. When kinetin in a solution of alcohol and carbowax is applied directly to the lateral buds of pea seedlings, it releases them from inhibition by the growing apex. It is shown that the role of alcohol in this solution is to act as a surfactant, permitting good contact with the buds, while that of carbowax, being hygroscopic, is to maintain a thin film of solution over the buds. Buds thus released from apical dominance by kinetin do not elongate as much as do uninhibited control buds. Such kinetin‐treated buds can, however, be made to elongate normally by the application of auxin locally to their apices. It is concluded that growing shoots are relatively insensitive to correlative inhibition because they synthesize two types of growth substances, namely, auxin, which antagonizes the inhibitory effect on internodal elongation, and cytokinins, which permit the apex itself to develop. In the discussion it is brought out that many cases of branching, which appear at first to bear little relation to one another, can be understood on the basis of two principles, namely: (1) Any reduction in the growth rate of a dominant apex reduces its inhibitory effect on other apices, and (2) once an apex starts growing it becomes less sensitive to inhibition by other apices These generalizations and the experimental results are tentatively interpreted in terms of an interaction between the syntheses of auxin and of cytoldnin.