98 Dr. H. Karsten on the Sexual Life of Plants. 



spores : these cells entirely occupy the intermediate space between 

 the two membranes, and each of them contains numerous endo- 

 genous cells. 



This fact of the breaking up of the integument of the Fern- 

 spores into three segments recalls our attention to similarly con- 

 structed pollen-grains, namely, to those in which the openings 

 in the extine are furnished with opercula, which are either simple 

 or cellular, smooth or setaceous. 



Three cell-like opercula, which occupy the whole circumference 

 of the pollen, are found in many Passiflorea? ; smaller ones, in 

 greater number, beset with seta?, belong to many other species of 

 this family, as well as to many Cucurbitacea?, &c. In the Cucur- 

 bitaceae, the opercula, besides being covered with setaceous 

 enlarged secretory cells belonging to the extine, are in their 

 formation evidently dependent on the " dot-cell " (intermediate 

 corpuscle) adjoining each operculum ; and in the Passiflorese it 

 is most probable that the very large " intermediate corpuscle " 

 actually constitutes the operculum. 



In the 51st plate of my ' Flora Columbia?/ I figured the pollen 

 of Passifiora servitensis, with its three very large opercula, 

 attached to the stigma in the act of protruding the intine. This 

 pollen shows that the different layers which Fritsche first ob- 

 served on the intine are not always lamina? of one and the same 

 cell-membrane, and that the actual intine is not always a cell of 

 the second generation, but may, in fact, be one of the third. 



Betwixt the two lamina? which hitherto have been together 

 regarded as the intine, a small " dot-cell " is observed, as in the 

 pollen of many Monocotyla?, whilst three such are met with in 

 the pollen of Ccelebogyne and of most Dicotyla?. Two sorts of 

 cells are thus formed in the extine, from one of which the fovilla 

 is separated, whilst the other appears intended to facilitate the 

 expulsion of the sister-cell from the mother-cell. From the re- 

 searches of Meyen and Schacht it also seems evident that the 

 pollen of Conifera? belongs to this category. 



It remains for future investigators to consider this relation of 

 the parts of pollen, and to decide, with regard to the different forms 

 of pollen, whether the opercula are immediately derived from the 

 " dot-cells," or from a portion of the extine as a consequence of 

 the contact of this with the " dot-cells." Both forms are met 

 with. That the "porous vesicles," which are frequently charged 

 with secretions, as well as the "dot-cells" may be transformed 

 directly into opercula, is not improbable ; nevertheless opercula 

 do also originate independently of these cell-structures in the 

 extine, the position and size of which are determined by the 

 contiguous " dot-cells," as for example in the Cucurbitacea?, 

 where the " dot-cell" (the "intermediate corpuscle" of Fritsche) 



