326 



ir. w 



ON THE MOEPHOLOGT OF 



accompanied by the formation of cell-plates, whieli, however, do not stretch completely 

 across the cell and are evanescent. Usually there is only one such division in the cell ; 

 •sometimes a second one follows, producing four free nuclei*. In the nucellar tissue 

 adjacent to the pollen-chamber the cells become disorganized, the nuclei of those which 

 are multinucleate fusing to a "formless mass." T^ie endosperm cells, especially those 

 of the jacket-layer, mostly become binucleate ; shortly before the cells are destroyed the 

 nuclei fuse f. In the endosperm cells lying further from the archegonia, an incomplete 

 nuclear fusion occurs not rarely, but here the nuclei entering into fusion do not lose 

 their individuality. The fact that the cells of the nucellus in the region most liable to 

 exhaustion undergo changes similar to those described for similarly situated endosperm 

 cells, leaves little doubt that we are here dealing with degenerating cells. The multipli- 

 cation of nuclei and their subsequent fusion are nutritive phenomena preceding the 

 destruction of the cell. 



Jaeger's X account of the multinucleate cells of the prothallus of Taxiis is of especial 



interest, since this is the case particularly referred to by Lotsy. Until June 



•ly 



July the prothallus is composed of uninucleate cells. Early in July, a month or more 



iftei^ fertilization, single cells become binucleate by indirect div 



cell-plat 



formed, but 



of short duration. About the middle 



contain as many as eight free 



f July some of the endosperm 



— thes^ having possibly arisen by direct d 



At the end of July cells with sixteen free nuclei are found 



are apparently in perfect condition. 



degeneration; they have decreased in size, have lost their spherical form, and hav 



. At this stao-e the nuclei 

 About the end of August they show signs of 



become 



Imassisr, zerrissen, aussrefranst 



o 



D 



At the beginning of September the 



nuclei in the endosperm cells beneath the growing embryo are usually reduced to one, 

 the rest to six or less. These have become further reduced in size and are of indefinite 

 form. Finally, the nuclei in each ceil fuse to form 4, 3, or 1 " Kernfleck" j|. These 

 processes occur first of all in those cells of the endosperm which are contiguous to the 



archegonia or 



the embryo. "Das diirfte wohl auf Embryovvirkun 



ickzufiihr 



sem. 



5> 



Here also we have a case of tissue-degeneration in which nuclear fusion represents 



Imost the final stage. It will also be noted that both 



Ephedi 



d 



Taxus the 



multinucleate condition is attained by a cell which was at first uninucleate 



The 



nuclear fusion which constitutes the primary endosperm cells of Gnetum and 

 Welwitschia is of a very diiferent character. The multinucleate character of the com- 



partments in which fu 



occurs is produced 



the primary septat 



of the 



Neither it nor the subsequent fusion can be held to be in any way influenced by the 

 activities of a parasitic organ or organism. The fusion is not one of a series of changes 

 leading to degeneration and death ; on the contrary, it inaugurates a new phase of growth 

 and subdivision, in the course of which a degree of organization appears in the tissue 

 produced ; for not only does it show a well-marked apical growth and regional distribution 

 of nutritive cells "f, but, in Gnetum, a differentiation into " a central region of smaller, 



• 



Jaccard, 1894, p. 34, fig. 48. 



§ Jaeger, 1809, t. 17. %. 29. 



t Stras"burger, 1880, pp. 106, 107. 



II Jaeger, 1899, t. 17. fig. 30. 



+ Jaeger, 1899. 

 f Pearson, 1909, p. 370 



