64 PART II. ANATOMY AND HISTOLOGY. [ 20 



only be accurately described as cellular when it consists of one or 

 more such cells, that is, when it is either unicellular (e.g. Yeast, 

 Hsematococcus, etc.) or multicellular. The body of an unseptate 

 plant (such as the Phycomycetous Fungi and the Siphonaceous 

 Algae), as also a segment of the body of an incompletely septate 

 plant (such as Cladophora, Hydrodictyon, etc.), is not a single cell, 

 but is an aggregate of protoplasmic units enclosed within a common 

 wall. Such a body, or part of a body, may be conveniently distin- 

 guished as a coenocyte, and the plants in which it occurs may be 

 said to have coenocytic structure. 



Even in typically cellular plants structures occur which are 

 coenocytic. Thus, in the early stages of its development in the 

 embryo-sac of a Phanerogam, the endosperm is generally unseptate, 

 consisting of a layer of protoplasm with many nuclei scattered 

 through it ; it eventually becomes a cellular tissue by the delimit- 

 ation of the constituent units by means of cell-walls. Again, 

 a " laticiferous cell " of a Euphorbia (and other Phanerogams) is 

 essentially a coenocyte like the body of a Vaucheria or a Botry- 

 dium. 



On the other hand, there is such a thing as a multinucleate cell. 

 It has been observed, for instance, in old internodal cells of Chara, 

 and in old parenchymatous cells of Lycopodium and of various 

 Phanerogams (e.g. Tradescantia, Taraxacum, Cereus, Solanum, etc.) 

 that, from being uninucleate, they become multinucleate by the 

 direct division or fragmentation of the nucleus. 



The distinction between a coenocyte and a multinucleate cell 

 would appear to be this : that the former is either multinucleate 

 from the first or becomes so at a very early stage in its develop- 

 ment, whilst the latter becomes multinucleate at a quite late 

 period. 



There is another kind of structure occurring in cellular plants 

 which has to be distinguished from both the cell and the coenocyte : 

 that is the syncyte. This structure is formed by the fusion of 

 already-formed cells, the cell-walls, when present, being more or 

 less completely absorbed, so that the cavities of the fused cells 

 becomec ontinuous. The commonest case of this occurs in the de- 

 velopment of vessels, where the transverse septa of a longitudinal 

 row of cells are absorbed so that a continuous tube is formed. 



But even in the fully-developed cellular plant-body it appears to 

 be very frequently the case that the protoplasm in one cell is not 

 absolutely cut off from that of the adjacent cells, but that there is 



