320 KirkKwoop: POLLEN-TUBE IN CUCURBITACEAE 
Amici,? in 1830, in a letter to Mirbel states that the pollen- 
tube gradually elongates, descending through the style, and comes 
into contact with the ovule, each ovule being reached by a sep- 
arate tube. 
Schleiden” (1844) traced the pollen-tube through the micro- 
pyle and point of the nucellus, even to the embryo-sac, in Pepo, 
Melo, Cucumis, Lagenaria and Momordica, and in the case of 
Momordica saw the germinal nuclei emerge from the pollen-tube. 
Recently Guéguen," in his studies on the comparative anatomy 
of the conducting-tissues of style and stigma, examined, among the 
Cucurbitaceae, Ecballium Elaterium, Cucurbita Pepo and Bryonia. 
He found the stylar canal present in Ecéal/inm, but obliterated in 
Cucurbita, but states that where the stigma is tetramerous the con- 
ducting-tissue presents an X-like structure as seen in transverse 
section of the style. This conducting-tissue he observed extended 
to the ovules, covering the surface of the placenta. He regards the 
Cucurbitaceae as very uniform in the matter of conducting-tissue. 
In 1902 Longo ® announced that the nutrition of the embryo 
in Cucurbita was performed by means of the pollen-tube. At the 
base of the neck of the nucellus the pollen-tube expands into a 
large bulla provided with branches which traverse the nucellus 
and the inner integument and proceed in intimate relation with the 
internal layers differentiated from the outer integument. Owing to 
a cutinization in the walls of the epidermal cells of the nucellus, as 
well as a suberization in the region of the chalaza, the embryo is 
soon cut off from the usual source of nutritive materials. The 
pollen-tube, with its branches rich in plasmatic contents and in 
starch, and with cellulose walls, furnishes the only points where 
fluids can enter the nucellus. Thus a haustorial function is as- 
cribed to the pollen-tube, which draws upon the inner layers of 
the outer integument, itself nourished by the vascular bundles. 
In the following year Longo” published the results of a more 
extended investigation, including thirteen genera and several more 
species. In all the cases examined the branching of the pollen- 
tube was found as a rule only in Cucurbita, though in all cases the 
course of the pollen-tube was always in accord with the distribu- 
tion of conducting-tissue. The formation of the bulla at the base 
of the neck of the nueelias is correlated with the presence of 
