KIRKWoOD: POLLEN-TUBE IN CUCURBITACEAE SSL 
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 (Zuffa maxima Hort.) when the 
starch is normal, in very small grains; it forms a bulla with 
numerous branches (Cucurbita) 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.’® 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 Cucurbitaceae, 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 Pepo 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 
Cucurbitaceae, viz.: Melothria pendula L., Micrampelis lobata 
(Michx.) Greene, and Cyclanthera explodens Naud. 
With a view to determining the length of time required for the 
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 ina 
few hours. If pollination is not effected the flowers remain open 
for several days. In Micrampelis and Cyclanthera the results were 
