Studies on the Bi7iucleate Phase in the Plant-cell. 19 



instance, of Eremurus himalaicus (e.g. PL I, fig. 1), which are 

 magnified to the same degree. This fact, and a certain difficulty 

 which is experienced in staining the nuclei satisfactorily, probably 

 accounts for the karyokinetic stages and phragmospheres having 

 been overlooked by Dr. McLean, who says, " Amitosis is the only 

 form of nuclear division which has been recognized in the tissues 

 investigated, and from its exceeding frequency in the constituent 

 cells it may be inferred that it is the only form occurring there." 

 In all Dr. McLean's figures the process of nuclear division is already 

 completed ; the fact that the pairs of nuclei lie close together does 

 not supply, as far as my experience goes, any evidence for amitosis, 

 since I have often observed the approximation of the paired 

 nuclei in cases in which their karyokinetic origin has been proved. 

 Elodea canadensis presents no essential differences from 

 Hippiiris vulgaris. In the region towards the apex of an axis 

 fixed on June 2, 1916, binucleate cells were numerous, especially 

 just above the nodes. Many nuclei were observed in mitosis 

 (PI. I, fig. 29), and phragmospheres occurred both in the cortex 

 and the epidermis (PL I, figs. 30 and 31). There appears to be no 

 evidence of amitosis, but I have seen some lobed nuclei (PL I, 

 fig. 32) which might at first sight suggest that direct division 

 was in progress. However from analogy with Asparagus and 

 Eremurus, in which I have been able to follow their history more 

 closely, I think that these lobed nuclei are probably merely senile. 



11. Stratiotes aloides L. (Text-figs 1, 2). 



In a note published some years ago* I gave an account of certain 

 cytological peculiarities observed in the roots of Stratiotes aloides, 

 the Water Soldier. Further work on this subject, in the light of 

 the results obtained in other connexions, has greatly modified the 

 conclusions there expressed. The principal feature to which atten- 

 tion was drawn was the constant occurrence of bilobed nuclei in 

 the tissues of the young roots, especially in the vascular cylinder. 

 Examination of further material has confirmed the view that this 

 lobing is natural and not artefact. Examples are shown in text- 

 figs. 1 and 2. A certain number of binucleate cells were also 

 observed — chiefly in the cortex — and it was supposed that amitosis 

 took place and that the paired nuclei arose through the bilobed 

 nuclei becoming nipped in two. But a further search through 

 material collected in two later seasons has shown that binucleate 

 cells arise in the root cortex of Stratiotes, just as in other cases 

 described in the present paper, by karyokinesis associated with a 

 phragmosphere. Owing to the small size of the cells and the 



* Arber, A. (1914). 



C 2 



