i2 Transactions of the Society. 



there was no sign of differentiation of vascular tissue, but the 

 phragmosphere observed occurred in the central region, which would 

 subsequently become the pith. In a series of sections through a 

 second axis, at a slightly more advanced stage than the first, a 

 typical phragmosphere with its paired nuclei was seen at about tlie 

 same distance from the apex — in this case slightly more than 



• 1 mm. In passing down the axis the binucleate cells become 

 rapidly more numerous. In an axis gathered on May 23 it was 

 "found that, at 1 cm. from the apex, binucleate cells were extremely 

 common in the pith, and trinucleate cells also occurred, while 

 occasional binucleate cells were seen also in the cortex. At 



1 • 5 cm. from the apex a large proportion of the pith cells had 

 become uninucleate. Binucleate cells, however, could be seen as 

 far from the apex as the ninth centimetre, but they steadily became 

 rarer, and in the tenth centimetre none were detected. Variation 

 in the length of the binucleate phase occurs in different shoots, for 

 in another axis of smaller diameter no binucleate cells could 

 be found even in the sixth centimetre. 



The young nuclei of Helianthiis Nuttallii are rounded, but in 

 the region in which the transition from a binucleate to a uni- 

 nucleate condition takes place a number of nuclei can be seen 

 whose appearance suggests fusion very strongly (PI. I, figs. 21 and 

 22). A form with two well-marked pointed lobes is decidedly 

 characteristic. Such cases as that drawn in PI. I, fig. 21, appear 

 however to invalidate the fusion interpretation, since a deeply 

 bilobed nucleus may sometimes be found in the same cell as a 

 second nucleus which is either normal or in a state of degeneration. 

 It is conceivable, though unlikely, that such a case might represent 

 the subsequent history of a trinucleate cell in which two nuclei 

 •are fusing and one degenerating. But besides symmetrically bilobed 

 nuclei, we also find examples of curiously elongated forms (PI. I, 

 fig. 23), and of lobing into two highly unequal parts (PI. I, fig. 24). 

 Such irregularity detracts very much from the probability of the 

 fusion hypothesis, and, as in the other cases here described, it 

 seems that the transition from the binucleate to the uninucleate 

 stage comes about by the degeneration of one nucleus (PI. I, 

 fig. 21), while lobing is merely a characteristic of the single nuclei 

 in the later stages of their career. But at the same time I feel 

 that in this case my preparations do not absolutely dispose of the 

 possibility that the " degenerating " nuclei may be artefact. 



4. Helianthus tuherosus L. 



Shoots of the Jerusalem Artichoke, Helianthus tuherosus L., 

 were examined for comparison with H. Nuttallii, and the behaviour 

 of the nuclei was found to be closely similar in the two cases. 

 Binucleate cells begin to occur very near the apex in H. tuherosus ; 



