38 COMPARATIVE EMBRYOLOGY OF THE RUBIACEAE 
and often do develop further, and undergo a simultaneous division 
(the first embryo-sac division), from which the actual physiological 
and morphological equivalence is inferred. 
THE BEHAVIOR OF THE POLLEN TUBE IN 
DIODIA AND RICHARDSONIA 
(PLATE 15) 
While engaged in the foregoing study of the embryology of 
certain Rubiaceae, namely, Diodia teres, Diodia Virginiana and 
Richardsonia pilosa, some conditions of rather more than usual 
interest attaching to the behavior of the pollen tube in these forms 
were met with. In view of the attention which the subject has of 
late received in some quarters—attention which has not by any 
means been barren of important results—it seems well at this 
time to present the outcome of acloser study of the phenomena in 
the above-mentioned plants, although the general subject in the 
Rubiaceae promises as a reward of future investigation further re- 
sults of interest. 
The flower in both genera presents the same chief features in 
common. The differences are chargeable to the different numer- 
ical relations in them, Diodia having a bicarpellary and Richard- 
sonia a tricarpellary ovary. This fact having been mentioned, 
we shall from this time on ignore it, since it has no bearing in 
particular upon the following description and for the sake of sim- 
plicity we shall take Diodia as the type. 
MORPHOLOGICAL RELATIONS OF THE STYLE 
The locules of the inferior ovary are separated by a partition 
of two portions, distinct in origin and in anatomical structure. 
The lower portion, or basal element, arises as a ridge from the 
floor of the ovary, and inserted on its margin are the ovules, one 
in each locule. This basal element reaches to somewhat less than 
one-half the depth of the ovary. The remaining distance is oc- 
cupied by a partition—the roof element—derived from the styles 
which growing out laterally from the upper part of the hollowed- 
out receptacles join at the middle point and grow upwards and down- 
wards to form the style. This consists therefore of two ( Diodia) or 
three ( Richardsonia) concrescent elements. The roof and floor 
