LEAKE AND RAM PRASAt). 45 



between plants of similar parentage remains obscure, and it has been 

 found impossible to predict its occurrence in any particular plant 

 or group of plants, and it appears to be a phenomenon quite distinct 

 from the two forms of sterility above dealt with. The solution of 

 the causes leading up to this fortuitous sterility is a matter which 

 has a considerable practical bearing on the raising of improved races. 

 That there lies here a field for cytological work* appears undoubted 

 but hitherto the oppoitunity for conducting such work with the 

 material to hand has been lacking. 



The frequency of cross -fertilisation in the field. 



(<■/) The strxrtiirc of tlie ffoiver. 

 The transference of pollen from one flower to another is, in general, 

 effected by one of the two agencies, wind or insects and the flower 

 is, further, frequently adapted to secure the services of a particular 

 agent. Considered from this aspect the cotton flower shows but 

 little adaptation. The petals are as a rule conspicuous and expand 

 widely, and the pollen grains are large and round and covered with 

 short papillae. Nectaries occur at the base of the petals and the 

 honey secreted by them accumulates outside the petals in the cup 

 formed by the gamosepaloas calyx and access to this honey is only 

 obtained through the narrow slit-like passages between the five pe- 

 tals. The above structural peculiarities are such as are commonly 

 associated with the visits of insects, and there is little doubt that 

 whatever cross-fertilisation takes place is the result of such visits. 

 On the other hand, the rupture of the anthers and consequent libera- 

 tion of pollen synchronise very closely with the maturation of the 

 stigma. During the cotton season the petals expand about 8 a.m. 

 and within thirty minutes of this expansion the pollen is liberated 

 and the stigma has become receptive. The pollen is at first sticky 

 but soon becomes dry and powdery and falls on the shghtest agitation 

 of the flower. Though the position of the flower is by no means 

 constant it is, perhaps, most commonly horizontal or pendent. The 



Cannon, Bull. Torrey liot. Club, XXX, It 03. 



