ii6 Journal of Agricultural Research voi. xvii. No. 3 



and typically are collapsed and shrunken. A few cell walls appear to 

 be broken. The cytoplasm is much contracted and drawn out into 

 irregular vacuolated strands. The nuclei are generally irregular in 

 outline and show evidence of disintegration. In many of the stigmas 

 the papillate cells are partly broken away from those beneath, and the 

 pollen grains are found among, or even beneath, the collapsed and partly 

 separated sheath composed of the tenninal cells. 



Heideman states (9, p. 191) that the "actual time during which 

 fertilization may be effected scarcely exceeds two hours." Obser\'ations 

 here show that under normal conditions the plum stigma remains recep- 

 tive for a maximum period of about one week. At the end of three to 

 five days, however, the stigma begins to turn brown, and as it becomes 

 dead and dry at the end of the receptive period the color gradually 

 deepens to a dark brown and then black. The dark color slowly extends 

 down the style, which, as a rule, abscisses before turning brown more 

 than two-thirds of the way to the abscission layer. In this way the 

 possible time of pollen-tube growth on the stigma is limited to a rela- 

 tively short period. The significance of this will be emphasized in 

 cormection with the discussion on the rate of tube growth. 



THE ACTION OF RAIN T-TPON THE STIGMA 



The prevailing belief among fruit growers is that the chief injury of 

 rain to the stigma, aside from washing pollen from it, is the dilution of 

 the stigmatic fluid to such an extent that the growth of the pollen tube 

 is prevented. Immediately after a heavy rain during full bloom on 

 May 9, 1 91 8, a study of stigmas under orchard conditions showed that 

 even those which were past the receptive stage, dark brown in color and 

 partially dead, were distinctly moist and turgid. 



Following these observations an investigation was made of the action 

 of water upon the stigma. When one which had been receptive for 

 about three days was dipped in water and carefully withdrawn, a small 

 droplet about the size of the stigma adhered. This droplet was absorbed 

 in approximately one minute. The dipping was repeated eight con- 

 secutive times in as many minutes, and in each case the droplet was as 

 quickly absorbed as in the first instance. As a result of the absorption 

 of water the papillate cells became distinctly turgid. A similar test was 

 made with an unreceptive stigma and also one which had passed the 

 receptive stage and of which the papillate cells had become dark brown 

 and partially dead. The same imbibition of water took place with 

 these two as with the receptive stigma. 



It will be evident that absorption of water in such quantities acts to 

 dilute the cell sap of the papillate cells. This, however, would appear 

 to be of no immediate consequence, since pollen does not take up the 

 stigmatic fluid until it is secreted, and even if pollen in this way came 



