POSITIONS AND MOVEMENTS OF 

 COTTON LEAVES 



How the Leaves Adjust Their Position to Varying Conditions of Illumination and 



of Soil Moisture 



R. M. Meade I 



THF leaves of the cotton plant are 

 cai)al)le of definite movements 

 which are made in direct reaction 

 to sunlight. The mo\ements of the 

 leaves are governed by the puhini in 

 the blade and petiole, similar to those 

 that determine movements in other 

 plants. While the results here reported 

 are of observations on phmts of Gos- 

 sypiiim hirsHtiim (Upland cotton) it 

 has been observed that similar reac- 

 tions occur in different degrees in other 

 species of Gossypium. 



SI/E AND SHAPE OF THE COTTON 

 LEAF 



The leaves of cotton seedlings are 

 entire, but as the plant grows older 

 there is a gradual change in leaf shape 

 until the final leaves of the mature 

 plants are deeply cleft with three to 

 seven palmate lobes. The blades are 

 nearly equal in length and width and 

 var>' from three to six inches in each 

 dimension, with the petiole or stem 

 about as long as the blade. The main 

 veins are very prominent, especially on 

 the lower surface of the leaf, and radiate 

 from the junction of the blade with the 

 petiole, extending to the tips of each 

 lobe. 



LOCATION, STRUCTURE AND FUNCTION 



OK THE TWO 0R(;ANS WHICH CONTROL 



LEAF MOVi:.MENTS 



The movements of the leaves in 

 res{)onse to light are controlled by two 

 organs Ujcated on the petiole of the 

 leaf. These organs are the basal pul- 

 vinus, situated at the base of the 



' .Ml characters, whether morphological or physiological, of an important cultivaterl plant 

 like cotton are of interest to hrceders. Little has been done in comparing related species and 

 varieties of plants in regard to their physiological characters and almost nothing is known of the 

 inheritance of such characters, excei)t as reg.irds resistance to diseases. An interesting subject 

 for investigation in this ditlicult held is siiggi-sied in this pajier which is based upon a manuscript 

 found among the (jajiers of the late K. .\L .Meade. —K. I), .\lartin. 



petiole, and the distal pulvinus, at 

 the end of the petiole. 



The basal pul\inus, visible extern- 

 ally as a thickening of the base of the 

 petiole, (See Fig. 7) differs structurally 

 from the rest of the petiole in having 

 less pith, more compact fibro-vascular 

 bundles, and more fleshy tissue sur- 

 rounding the bundles. Frequently the 

 pulvinoid tissue attains an inch and 

 a half in length and a diameter twice 

 that of the rest of the petiole. Often 

 there is no definite distinction between 

 the pulvinus and the petiole proper, as 

 the pulvinus tapers gradually to the 

 diameter of the rest of the petiole. 

 Sometimes, however, the change in 

 size is more abrupt and distinctly 

 marked. The function of this pulvinus 

 appears to be that of controlling the 

 movement of the petiole. 



The distal puhinus is composed of 

 the upper part of the petiole ending 

 with a callus or cushion at the junction 

 of the principal veins of the leaf. The 

 pulvinoid tissue of the upper portion 

 of the petiole is generally not more 

 than half an inch long and scarcely 

 thicker than the middle of the petiole. 

 A special feature of the distal puhinus 

 is at its attachment to the blade where 

 it is contracted, leaving very little 

 tissue around the bundles of the stem. 

 The constricted portion acts as a 

 pivot on which the blade may swing 

 without greatly altering the position 

 of the petiole. 



The veins ma\' be distinctK- thick- 

 ened for a distance of three-fourths of 

 an inch from the base, and dislin- 



444 



