THE DEVELOPMENT OF THE FRUIT 



527 



In discussing the influence of nutritive conditions within the plant 

 on fruit setting attention has been directed to their influence on 

 parthenocarpy. Apparently unusual accumulation of elaborated foods 

 in proximity to flowers in the receptive stage often acts as a stimulus to 

 further growth and development and in this way inhibits the formation 

 of an abscission layer much as would the stimulus occasioned by the 

 stings of certain insects or by developing seeds. 



Relation of Anatomical Structure of Fruit to Parthenocarpy. — As 

 has been pointed out, seedlessness is to be expected at least occasionally 

 in almost every species and variety and it is probable that the same may 

 be said of parthenocarpy. It may be noted, however, that it is more 

 frequent in species whose fruits the botanist classifies as inferior, those 

 into whose structure tissues other than the ovary enter. Though this 

 may be a mere coincidence, it at least suggests that the greater stem-like 

 character of such fruits imparts to them a stronger tendency to persist 



Fig. 55. 



-Developing fruits of the LeBrun pear; a and d normal seed-containing 

 fruits; b, c, e and / seedless. (After Muller-Thurgau.^'') 



than there is in those whose tissues when mature are entirely carpellary 

 in nature. They seem to be less in need of the stimulus of fertilization. 

 In Fig. 55 are shown pears of the LeBrun variety, one of which is develop- 

 ing as a result of the stimulus afforded by pollination and fertilization. 

 The other two are developing parthenocarpically. The greater develop- 

 ment of the stem tissues in the latter case is very suggestive. 



Suggestive also in this connection are the following statements by Johnson^* 

 on the perennation and proliferation of the fruits of Opuntia fulgida. "It is 

 true that the vegetative joints and both the fertile and sterile fruits resemble 

 each other greatly in their capacity for proliferation. There seems no adequate 

 reason, however, for assuming that either the proUferating habit or the fimda- 

 mental structure of the fruit is a secondary thing in the evolution of the opuntias. 

 On the contrary, it is natural that the thick-skinned, water-stored joints of 

 these cacti should have proved capable of persisting on moderately moist soil 

 until rooted deeply enough to secure a water-supply adequate for the starting 

 of a young plant. The fruit being . . . really a stem in organization, up to 



