Studies on the Binucleate Phase in the Plant-cell. 11 



into a phragmosphere which ultimately became merged in the 

 general cytoplasm, so it is difficult to see what apparatus could be 

 brought into play at a later stage to produce a wall. This leaves 

 us with a third alternative, which appears to have most in its 

 favour. There are indications that, of the pair of nuclei within a 

 single cell, one is apt to become senile more rapidly than the other^ 

 and we sometimes see a cell containing one nucleus in fair preser- 

 vation, while the other is smaller, somewhat dense, and possibly in 

 process of disappearance. But we have been imable, in spite of 

 repeated attempts, to get really critical evidence on this point, and,, 

 though the degeneration of one nucleus seems the most probable 

 method by which the transition from two nuclei to one is brought 

 about, we cannot regard it as definitely proved. 



Since the above account of Asparagus officinalis was written, a 

 recent paper by Schiirhoff* on nuclear fusions in the shoot apex of this 

 plant has come to our notice. This author seems to have overlooked 

 the multinucleate condition of the ground tissue in general, but he 

 describes the occurrence of " nuclear fusions " in the cells at the 

 periphery of the vascular bundles, after these have become bi- 

 nucleate. He states that he has not determined the origin of the 

 binucleate condition in the younger stages, but that in older stages 

 it occurs through the breaking down of the partition walls between 

 adjacent cells. I have examined more than a hundred hand and 

 microtome preparations, stained in various ways, made from nine 

 shoots of Asparagus, mostly of the age of those used by Schiirhoff^ 

 gathered in two successive years, and fixed on the spot with 

 chrom-acetic or alcohol acetic, but I have never observed any in- 

 dication of the breaking down of walls or of nuclear migrations- 

 such as he describes. On the contrary, I have seen paired nuclei 

 with phragmospheres in the ground-tissue cells at the periphery of 

 the vascular bundles, which are apparently the elements to which 

 he refers ; thus, the origin of the binucleate condition is precisely 

 the same here as in the rest of the ground tissue. The " fusions '^ 

 which he describes are no doubt the lobed nuclei whose significance 

 we have already fully discussed. 



3. Helianthus Nuttallii Torr. et Gray (PL I, figs. 21-24). 



Young axes of the Perennial Sunflower, Helianthus Nuttallii^ 

 were examined at stages at which the rudimentary inflorescence- 

 was just 'becoming differentiated within the terminal bud. 

 Binucleate cells and phragmospheres were found to make their 

 appearance remarkably near the tip ; in the case of one axis^. 

 which was cut into serial sections, the first phragmosphere was 

 seen at less than • 1 mm. from the extreme apex. At this level 



* Schiirhoff, P. N. (1916). 



