330 Kirkwood : Pollen-tube in Cucurbitaceae 



Amid, 2 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. 



( 



Pep 



Melo, Citciimis, Lagenaria and Momordica, and in the case of 

 Moviordica saw the germinal nuclei emerge from the pollen-tube. 



Recently Gueguen, 11 in his studies on the comparative anatomy 

 of the conducting-tissues of style and stigma, examined, among the 

 Cucurbitaceae, Ecballium Elaterium, Cucurbit a Pepo and Bryonia. 

 He found the stylar canal present in Ecballium, 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 18 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 1T 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 nucellus is correlated with the presence of 



