87 



dermal cell-layers, and is continuous transversely, as well as 

 longitudinally. 



The tissue consists, moreover, of small sub-isodiainetric cells, 

 rich in contents, and not lengthened in any direction in partic- 

 ular. They lack, therefore, the anatomical characters found gen- 

 erally in stylar conductive tissues, and are in form, at least, like 

 the cells which lie in portions of the path of the pollen tube in 

 Casuarina, certain Amcntiferae, Alckcniilla and in a number of 

 other plants.* 



The conductive tissue is further extended between the ovules, 

 being interrupted by their funicles, and comes to abut npon their 

 nucclli. This is brought about by the circumstance that in 

 Cncurbita Pcpo the nucellus has tlie shape of a flask, the long 

 neck of which extends through and protrudes beyond the micro- 

 pyle, its end coming into contact with the conductive tissue. It 

 thus comes about that there is, in this species, no free locnlar 

 space, but rather a continuous stretch of conductive tissue from 

 the stigma to the embryo sac. What would be inferred, namely, 

 that the pollen tube must therefore have a completely mtercel- 

 lular course, is indeed the case, as Longo has demonstrated. 



In the other genera studied, on the other hand, e. g., Citrullns 

 vulgaris, Schrad. (which Longo figures), the nucellus has but a 

 short neck, which leaves open a micropylar canal of considerable 

 extent. From these, too, is absent the conductive tissue de- 

 scribed for Cncnrbita Pcpo, there being instead an ovarian space. 

 Through this, and through the micropyle, the pollen tube grows 

 freely in its path to the nucellus, where, however, as in many 

 other plants, it must enter upon a short intercellular course in 

 order to reach the embryo sac. It thus appears that, /// tivo 

 closely related genera in the same family, and indeed in different 

 species of the same genus, the pollen tube differs in its behavior, in 

 that, in the one case its course is throughout intercellular, ivhile in 

 the other it moves freely in a cavity. 



In every other species of this genus, Cncurbita, the nucellus is 

 too short to reach quite up to the conductive tissue {e. g., C. 

 maxinui, ficifolia, foetidissimd) and in these, the pollen tube 



* For citations of tlie pertinent literature, see either of the papers above indicated. 



