THE STRUCTURE OF CELLS 5 



and others have abundantly emphasised and justified these far- 

 reaching generalisations. 



But with the improvements which have been effected in 

 technique during the last quarter of a century, new facts have 

 come to light which have somewhat modified the conception of the 

 cell as held by the earlier writers. It has been already seen how 

 the centre of gravity gradually shifted from the cell-wall to the 

 cell-contents, and that, as Max Schultze declared, the essential 

 constituents of the cell were represented by the protoplasm and the 

 nucleus, the wall being of altogether subordinate importance. The 

 discovery that masses of protoplasm might contain not one but 

 many nuclei, and that such a condition is not uncommon both 

 amongst various groups and tissues in plants and animals, appeared 

 to some writers to present a difficulty in accepting the cell theory 

 as treated above, and various explanations have been offered in 

 order to bring these cases into line with the theory as more 

 generally understood and defined. Such organisms or tissues 

 have been termed non- cellular a negative and unsatisfactory 

 expression which has been replaced by the more appropriate word 

 syncytium or coenocyte. These words emphasise the view that, mor- 

 phologically, the individual units, which collectively make up the 

 syncytial tissue, are not isolated from each other by definite 

 barriers. Sachs proposed the term energid to express the cell in 

 Max Schultze's sense, meaning thereby the nucleus, together with 

 the portion of protoplasm dominated by it. Essentially this is 

 a physiological definition as contrasted with the morphological idea 

 embodied in the word syncytium. And it is, on the whole, a legiti- 

 mate expression, since it really does correspond to a fact. Moreover, 

 it has the merit of being equally applicable to the cases of isolated 

 cells as well as of those in which such limits are not structurally 

 traceable. The objection raised to the conception underlying it, on 

 the ground that the nucleus of a syncytium does not always dominate 

 the same protoplasm, is not a valid one, inasmuch as it is quite 

 possible perhaps even probable that an essentially similar state 

 of things also obtains even in those tissues in which the constituent 

 cells are apparently isolated. For it has gradually been proved for 

 a very large number of cases that the protoplasm of adjacent cells is 

 in actual physical continuity through the fine pores present in the 

 delimiting cell-walls. It is tolerably easy to observe this continuity 

 in the epithelial cells of some amphibian tissues, and there is a con- 

 siderable weight of evidence to show that it is far more general than 

 was generally supposed to be the case. In plant-tissues also it has 

 been repeatedly demonstrated since its first discovery by Tangl (in 

 1879)in the endosperm of certain seeds. Gardiner and Russow almost 

 simultaneously demonstrated its existence in the tissues of several 

 adult plants in 1883, and since that time it has been clearly proved to 



