KlRKWOOD : PoLLEX-TUBE IN CuCURBITACEAE 331 



starch in the same neck. He found no expansion of the pollen- 

 tube when the nucellus contained no starch ; it forms simply a 

 bulla without much branching {Lnffa maxima Hort.) when the 

 starch is normal, in very small grains ; it forms a bulla with 

 numerous branches {Ciicurbitci) when the starch is abundant in 

 large grains, often in the form of amylo-dextrine. He concludes 

 further that the course of the pollen-tube is regulated by partic- 

 ular substances which act in a chemotactic fashion ; in this conclu- 

 sion, agreeing with Lloyd. 16 When these substances are devel- 

 oped in the interior of the tissues it (the tube) has an endotropic 



course ; when on the exterior an ectotropic course. 



In an earlier article the writer made reference to the behavior 

 of the pollen-tube in some of the Cuciirbitaccae, and the phe- 

 nomena observed in certain cases seemed worthy of further investi- 

 gation. In most cases studied the pollen-tube presented no unusual 

 conditions, but in a few instances the dilation or branching of the 

 tube in the neck of the nucellus was a conspicuous feature. In 

 Cucurbita Pcpo the facts recorded by Longo were observed, and 

 in other genera was noted a tendency similar, though less marked. 

 The present study deals particularly with three members of the 

 Cuatrbitaceae, viz.: Melothria pe.ndula L., Micrampelis lobata 



tplodens 



With 



pollen-tube to traverse the intervening tissue between the stigma 

 and the embryo-sac, recourse was had to the following methods : 

 Buds of the pistillate flowers about to open were covered with 

 small bags of tissue paper tied about the peduncle. This was 

 done usually between 4 and 6 o'clock P.M., and the flowers were 

 usually found open the next morning. The stigmas were then 

 pollinated and the bag replaced. At different intervals of time 

 after pollination the fruits were collected and fixed in separate lots 

 for study. Some were also examined fresh by means of freehand 

 sections. In such preparations the pollen-tubes were easily 



recognized. 



The effects of pollination were apparent soonest in the case of 

 Melothria, in which the corolla-lobes close in over the stigma in a 

 few hours. If pollination is not effected the flowers remain open 

 for several days. In Micrampelis and Cyclanthera the results were 



