Multinucleate Cells : An Historical Study (1879-1919). 27 



transverse walls are resorbed, and the characteristic sculpturing 

 is formed. • 



In several species of Euphorhia and Bicinus, the young plerome 

 elements of the root, destined to form the segments of the vessels, 

 were observed by Smolak'(1904) to be quadrinucleate. He found 

 that the plurality of nuclei in the vessel initials arose by mitotic 

 divisions which were not followed by cell divisions or wall- 

 formation. The four nuclei sometimes fused into one long nucleus, 

 e.g. Euphorhia Lathyris, but in Bicinus fusions were less frequent. 



Nemec (1910) six years later made a comprehensive study of 

 the multinucleate vessel rudiments and plerome cells of Bicinus. 

 He likewise found that the nuclei arose by karyokinesis. A 

 spindle is produced between the nuclei at each division, but this 

 breaks down at an early stage, becomes granular, and soon 

 disappears altogether. From two to sixteen nuclei may be found 

 in a single cell, generally arranged in a longitudinal row. Nuclear 

 fusions may occur, but Nemec regards them as rare. 



We have now to consider that group of papers on multinucleate 

 parenchymatous cells which includes the most recent work on the 

 subject. Twenty years ago, one of us (Beer, K., 1899) recorded the 

 fact that multinucleate cells of a very pronounced character occur 

 in the stem and leaf-sheaths of a number of Graminese. He found 

 this to be the case in Zea Mays (stem, leaf-sheath and root), Secale 

 cereale (leaf- sheath), Triticum vulgare (stem and leaf-sheath), 

 Hordeuni sativum (leaf-sheath), and Dactylis glomerata (leaf-sheath). 

 He called attention to the fact that it is in young, still active 

 tissues that the multinucleate condition is most marked. 



In 1914 Dr. E. C. McLean published an account of his 

 observations upon amitosis in the parenchyma of water plants. 

 He found that nuclei which he regarded as having arisen through 

 direct division were frequently to be found associated in pairs in 

 the same cell, while, moi-e rarely, three nuclei might be met with 

 in one cell. Certain stages, which the author regards as represent- 

 ing the actual separation of the two daughter nuclei, were observed. 

 According to McLean's description, no constriction occurs, but 

 the process resembles the longitudinal fission of the Flagellata. 

 His observations relate to eight aquatic species, including both 

 Dicotyledons and Monocotyledons, as well as to two land plants, 

 Dionsea muscipula and Polypodium ireoides. He believes that 

 cell-division may follow the amitotic division of the nucleus, but 

 he does not describe this in any particular case. We chose two of 

 McLean's cases for re-examination {Hippuris and Elodea), and 

 although we can confirm his record of multinucleate cells in both 

 plants, we find that the nuclei in question invariably arise by 

 mitosis and not by direct division.* 



* Arber, A. (1920). 



