355 



pairs, points to a verj strong affinity which cannot be broken bj 

 the individual splitting. 



In the division of tiie einbrjosac-inother-cell and the pollen-tnother- 

 ceil of the E. inolaceo-petlohita we have tlie same phenomenon again 

 as was also seen in vegetative cells, namely the segmentation of 

 the chromosomes. It is remarkable, however, that here the chro- 

 matic particles lie in pairs, as we find all the chromosomes in the 

 two other subspecies in psendo-gemini. Here too very large num- 

 bers were found ; approximately 50, 64, 70 and even as high as 

 130 or 140 were found. Fig. 8 represents such a stadium taken 

 from a pollen-mother-cell, which had been cut into three sections, 

 only one of which is shown here. Nevertheless about 60 chromo- 

 some parlicies can be counted. As the embryosac-mother-ceil has 

 exactly the same appearance and as here too the same phenomenon 

 is seen directly after the division, it was impossible to find a pair 

 of daughter nuclei with the diploid number to prove apogamy. 

 Here, however, some very distinct endosperm-divisions lend assistance. 

 As it was established that the polar-nuclei unite with each other in 

 this apogamous plant also, the endosperm-nuclei must possess twice 

 as many chromosomes as the embiyosac-nuciei. Thus, to demonstrate 

 apogamy this number would have to be 24, and that this is actu- 

 ally the case is siiown by fig. 7, which illustrates a cross-section 

 through the middle of one spindle, looking in the direction of one 

 of the poles. The ends of the 24 chromosomes can be clearly 

 distinguished, while the attraction of some chromosomes by the 

 poles can also be observed. 



Whereas in the divisions of the embryosac-mother-cell there is no 

 reduction of the number of chromosomes, even though it has passed 

 from the heterotypic phase to the homoiotypic very shortly before 

 the division, the reducing division in the pollen-mother-cells occuis 

 normally. During this division no peculiarity was observed in 

 any of the cases examined other than the segmentation above-men- 

 tioned in E. violaceo-petiohita. Fig. 9 represents 2 sections of the 

 tetrad nuclei of a pollen-mother-cell of E. cochleoides, all of which 

 form the reduced number of chromosomes. 



As has been said, however, the great majority of the pollen-grains 

 produced from them are sterile. But even if there be fertile ones 

 among them, they are not productive. 



Thus tiie most important conclusion arrived at was that apogamy 

 occurs in these three elementary species of Erophila, which explains 

 the failure of tiie attempts at cross-fertilization. The experiments of 

 Rosen have shown that not all subspecies are apogamous, or at 



