60 PHYSIOLOGICAL MORPHOLOGY 



of a multicellular organism. So marked a differentiation of labour is 

 impossible in unicellular plants, although in very large multinucleate forms, 

 and especially in those such as Caulerpa, &c., which stand on the border- 

 land between unicellular and multicellular plants, a segmentation into root 

 and shoot, &c. may take place, even although the rotating endoplasm travels 

 continually through all parts. 



Following the usual nomenclature, we may call each distinct individual proto- 

 plast a cell, independently of whether it is surrounded by a cell-wall (dermatoplast) 

 or is naked (gymnoplast). Unicellular protoplasts may, using the nomenclature 

 put forward by Hanstein 1 , be termed monoplasts, multinucleate protoplasts, sym- 

 plasts. The Siphoneae and other multinucleate protoplasts are to be regarded as 

 unicellular plants, not as non-cellular plants, as suggested by Sachs 2 . 



Since the terms cell and protoplast definitely indicate the combination of 

 nucleus and cytoplasm, it seems hardly necessary to introduce the term energid to 

 represent the combination of a nucleus and cytoplasm which forms the living cell 

 unit. To call a protoplast an ' energid ' will not make it any easier to understand 

 its nature and vital mechanism. Sachs seems to state explicitly that in multi- 

 nucleate cells each energid is to be regarded as a definite whole, even though no 

 visible line of demarcation exists 8 . It is, "however, hardly credible that a multi- 

 nucleate cell is made up of a series of energids, in each of which the living 

 substance remains separate and distinct from its neighbours, and indeed it may be 

 directly seen that the cytoplasm in the neighbourhood of each nucleus is continually 

 changing when streaming takes place, while if the nucleus rotates also, it is con- 

 tinually being associated with new portions of the non-moving ectoplasmic layer. 

 Moreover it is quite certain that the cytoplasm lying between a number of nuclei is 

 influenced by all of them to an extent corresponding to their respective distances 

 from it, so that all these considerations compel us to regard a multinucleate cell as 

 a single unit, both morphologically and physiologically. 



[It will be noticed that the discussion of this essentially morphological 

 question from a purely physiological point of view creates considerable con- 

 fusion. The word ' cell ' has such widely different meanings attached to it that it 

 seems inadvisable to use it as a scientific term of restricted application. In the 

 widest possible sense, any differentiated mass of plasma with or without a cell- 

 wall, with one or with many nuclei will constitute a cell, while a protoplast is 

 formed by the symbiotic union of a single nucleus and a single plasma mass only, 

 and represents the lowest unit capable of separate existence, for that non-nucleated 

 forms exist at the present day is doubtful. A typical vegetable cell will therefore 

 be composed of a cellulose vesicle enclosing a single protoplast. A number of 

 protoplasts may be united together to form a multinucleate coenocyte, which may 



1 Hanstein, Bot. Abh. 1880, Bd. iv, p. 9. 



* Sachs, Ueber einzellige Pflanzen, Sitrungsb. d. Phys.-Med. Gesellschaft zu Wurzburg, 1878. 

 3 Sachs, Flora, 1892, p. 57 ; ibid., 1895, Erg.-bd. p. 406. See also Zimmermann, Bcihefte z. 

 Bot. Centralbl., 1893, Bd. in, p. 207; Strasburger, Histologische Beitrage, 1893, Bd. V, p. 108. 



