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94 CoMPARATIVE EMBRYOLOGY .OF THE RUBIACEAE 
In this part of its course the pollen tubes which are usually to 
be found in numbers produce a destructive effect upon the cells, 
upon which they impinge. The effect has the appearance of be- 
ing due to mechanical pressure owing in part to the number of 
tubes present, and in part to their larger diameter. The contents 
of the conductive cells thus affected appear homogeneous and 
deeply staining and the nuclei lose their normal appearance, while 
the cells are crushed out of shape (fig. 4). The effect of the tube 
is unequal, destroying cells, now here, now there, without any dis- 
solution of the walls, showing at once the difference between a 
mechanical operation, and one involving the histolysis of the cir- 
cumjacent tissue as by digestion. 
The behavior of the pollen tubes when they reach the sub- 
epidermal parenchyma of the basal partition is quite uniform, and 
is strongly suggestive of a purely mechanical influence. In the 
case of Richardsonia there is formed at that point by virtue of the 
confluence of the funicles of the three ovules, a basin so to speak, 
filled with the isodiametric irregular conductive cells. Should we 
plant a seedling in a basin of soil the roots would penetrate till the 
walls of the basin had been reached, and they would then glide 
along the walls. Such a case appears to be quite analogous to 
the one before us, excepting that geotropism plays no part in the 
behavior of the pollen tube. In Diodia teres the penetration of 
the epidermis of the basal partition does not take place as in 
Richardsonia ; but rather the tubes bend upward in the irregular 
cells of the stylar conductive tissue, passing at first between the 
walls of the style and strophiole, but soon penetrating the columnar 
epidermis of the latter ) fig. 8). 
Having now reached the thick-walled epidermis, the pollen 
tube travels along till it enters the regular thick-walled columnar 
cells which constitute the collar of connective tissue about the 
funicle and the strophiole. It then passes out of the fusion tissue 
and travels in a fairly direct path upwards, that is toward the 
chalazal region of the ovule (text figs. 8 and 9). It gradually 
toms, however, so as to pass around one side or the other of the 
TA us m finds itself in the epidermis of the lower side of 
de ae 9 t this time the course is more or less irregular, and 
sometimes branches te 0 Occasionally in the 
