332 KirKwoop: POLLEN-TUBE IN CUCURBITACEAE 
not immediately apparent, only those parts of the stigma upon 
which the pollen germinated showing any change. Under normal 
conditions the pistillate flowers of JJe/othria are pollinated early 
in the morning from staminate flowers which open the same day. 
The staminate flowers are very ephemeral and fall off usually in a 
few hours. 
The effects of pollination and fertilization in the Cucurbitaceae 
have been carefully studied by Massart,!” who experimented with 
Cucurbita, Bryonia, Ecballium and Thladiantha. He finds that the 
excitation which determines the survival and the beginning of the 
increase in the size of the fruit of Cucurbita Pepo is derived from the 
pollen itself and may be replaced by a traumatism ; but that the 
excitation which provokes the general increase in the fruit proceeds 
only from fertilized ovules. The placentae, however, do not 
develop except in the vicinity of the fertilized ovules. 
As to the time required for the pollen-tube to reach the 
embryo-sac, considerable variation was observed, the time vary- 
ing twenty hours or more, depending on the number and position 
of the ovules. After twenty-six hours the pollen-tube was 
observed in the nucellus of Me/othria and the same condition 
appeared in Micrampelis after nineteen hours from the time of 
pollination. In Cyclanthera no tubes were observed at the ovules 
until forty-one hours had elapsed. Most of the distance between 
the stigma and the embryo-sac is traversed by the pollen-tube in 
three or four hours. During this time the tube has passed 
through the style and into the ovary. The growth is much 
slower as the tube nears the micropyle. This feature seems to 
be correlated with the amount of available reserve food in the 
tube, which is of course greatest at the beginning of its growth. 
In the Cucurbitaceae the form and structure of the ovary 10 
different genera varies a good deal, but in most cases the cavity 
of the ovary is practically filled by the fleshy development of the 
placentae and the pericarp. A fusion of the ingrowing lobes of 
the placenta often occurs (Cucurbita, Citrullus) and leaves no space 
between them. In a similar way the stylar canal may also be 
obliterated. In Melothria, Micrampelis and Cyclanthera, however, 
such fusion does not take place before fertilization. The structure 
of the ovary in Melothria is similar to that of Cucurbita, excePt 
