Kirkwood : Pollen-tube in Cucurbitaceae 329 



orchids, the difference in time being in no relation to the distance 

 traversed. Among woody plants the time between pollination 

 and fertilization has been observed to vary from one month 

 (Betu/a s ), to several months {Hamamclis)' M \ and Conrad 7 has 

 shown that it is over a year in Qucrcus. It has been shown that in 

 those cases where a longer time is required the pollen-tube passes 

 through a more or less protracted resting period ; in these cases 

 also the branching of tubes is more or less common, as appears in 

 Pinus and the other cases above cited. 



Another phase of the development at this stage which has not 

 received sufficient attention is the effect of the pollen-tube itself on 

 the formation of the fruit, or the effect in some cases of a mere irri- 

 tation of the stigma. Gaertner 10 reports that with certain plants he 

 was able to obtain sterile fruits as large as normal ones by apply- 

 ing to the stigmas the spores of Lycopodium. Tschermak 3 - reports 

 various cases in the enlargement of the ovary by the use of pollen 

 which did not fertilize the seed. Massart ]9 secured partial develop- 

 ment of fruits in certain Cucurbitaceous forms by applying tritur- 

 ated pollen to the stigmas. In these cases no seeds were fertilized 

 and it appears that the pollen is the seat of an excitant which pene- 

 trates the stigma and determines the survival of the ovary. Fur- 

 thermore Leclerc du Sablon M has found that the crossing of melons 

 and cucumbers results in a considerable modification of the quan- 

 tity and quality of the carbohydrates in the placenta and the 

 pericarp. 



The Cucurbitaceae have long been under the observation of 

 botanists, and certain features in the development of their fruit 

 have frequently attracted attention. Soon after Amici's discovery 



of the pollen-tube of Portulaca olcracea 1 (1823), Brongniart 5 



(1826) described a cellular conducting tissue in Cucurbita maxima 

 Duch. and showed the pollen-tube traversing the beak of the nu- 

 cellus. He observed that the u spermatic granules " were trans- 

 ported by a canal formed of the intercellular spaces of the tissues 

 of the pistil. ' 



Gaertner, 1 ' in 1827, made observations on a number of plants 

 and reported an acid secretion from the stigma in certain cases at 

 the time of maturity, and also a correlation between the amount of 

 pollen on the stigma and the number of seeds produced, and that 

 the number of seeds was increased by cross-fertilization. 



