264 SUMMARY OF CURRENT RESEARCHES RELATING TO 



arvensis and Primula sinensis and elatior) the free central placenta is 

 united with the stylar canal by a cone of condi;cting tissue projecting 

 from the placenta into the canal. The pollen-tubes, after descending 

 the stylar canal, are taken up by this cone, and conducted to the 

 micropyle over the papillose surface of the placenta. 



The following may be stated as the general results reached by 

 Detmar's observations. The growing pollen-tubes receive their forma- 

 tive materials from the mucilaginous and amyloid substances secreted 

 by secreting organs on the stigma, and in the stylar canal and interior 

 of the ovary. These secreting organs are more or less papillose, 

 varying in form from a small projection to a long hair, and are 

 usually unicellitlar, though sometimes multicellular. The stigmatic 

 papillae are, as a rule, longer than those of the ovary, since they also 

 provide a detaining apparatus for the pollen ; but their contents are 

 apparently identical with the metaplasm of the colleters and nectaries. 

 Besides providing nutrition for the pollen-tubes, these papillose 

 structures furnish also a conducting tissue, to guide the pollen-tube, 

 when it has reached the cavity of the ovary, to the micropyles of the 

 ovules. The position of this conducting tissue within the ovary 

 depends on that of the micropyles. A conducting tissue of a similar 

 nature may occur on the internal walls of the ovary, on the funiculus, 

 and even on the integuments of the ovule, the same physiological 

 functions being performed by structures of very different morpho- 

 logical value. Seeing that this tissue reaches up to the very micropyle 

 itself, and that it only can supply the pollen-tube with the nutriment 

 it requires, it follows that the entrance of the pollen-tube into the 

 ovule is a purely mechanical phenomenon, and does not depend on 

 any mysterious relationships between the pollen-tube and the 

 embryo-sac. 



Nucleus of Vegetable Cells.* — Treub states that in the older 

 cells in the neighbourhood of the vascular bundles of the leaf-stalk 

 of OpJiioglossum vulgatum and Botryehium Lunaria are nuclei, which 

 are of no regular form, but have more or less deep indentations, 

 causing them to be lobed or constricted. The constriction sometimes 

 goes so far that in optical section the nucleus appears completely 

 divided in two ; but focussing always shows the parts to be united by 

 a thin strip, no actiial division of the nucleus taking place. But in 

 other cases — like the large cells of the internodes of Cliara, as 

 Schmitz and the writer have already observed — a complete division 

 is etfected. A fresh illustration of this " fragmentation," in contrast 

 to normal division, was observed in the endosperm-cells of the 

 embryo-sac of Imatophyllum cyrtanthiflorum, where various stages of 

 the process may be observed in the same preparation. 



Not only in the nuclei of multinucleated cells, and in free cell- 

 formation, does a simultaneous division of nuclei take place, but in 

 an entire group of cells in the endosperm of Imatophyllum cyrtantlii- 

 Jlorum the division of the nuclei takes place simultaneously. This 



* Arch, de Biol, iii. (1880) pp. 393-404 (1 pi.). See Bot. Ceutrulbl, ii. (1881) 

 p. 106. 



