August, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



513 



The Study of the Cell 

 in the Higher Plants. 



By H. A. Haig. 



There are few things more interesting in the science 

 of botany than an insight into the ultimate structure 

 and vital processes presented by the cell; and in this 

 article I shall endeavour to make clear some of the 

 more important functions and structural details to be 

 made out in those cells which are met with in the more 

 highly differentiated members of the vegetable king- 

 dom. It is, however, to be borne in mind that living 

 cell-units may in all cases be reduced to one or more 

 simple types, and that there is no essential difference in 

 function between a cell from the assimilating tissue of 

 the cortex in a higher plant, and that from a filament 

 of an Alga, although there may be some difference in 

 structure, in order to cope with surrounding conditions. 



It will, perhaps, be well, first of all, to state con- 

 cisely what we have to examine in any given cell, in 

 order, and thr:n to take each one of these and study it 

 separately; and, finally, to sum up the attributes of the 

 cell, and from this to try and gain some idea of the 

 general value of the organism considered as a co- 

 worker with others of the same kind. 



In any given cell we shall have to study : — 

 I. — The general microscopical structure. 

 2. — The reaction of the cell to stimuli of various 



kinds. 



3. — The reproduction of similar cells from pre-ex- 

 isting ones. 



4. — The further modification of a cell as dependent 



upon its position and the functions it has ultimately 



to fulfil. 



Further, I shall endeavour to compare the results 

 of our observations with those arrived at by some of 

 those biologists who' have made the cell their special 

 study. [Of the figures that illustrate the text, some 

 are drawn from actual observation, and others are 

 photo-micrographs. The methods of staining and pre- 

 paration will not be gone into very fully, as space docs 

 not allow.] 



I. — The general microscopical structure. 



A cell from a growing-point, such as a stem apex or 

 root-tip, serves very well for. the study of structure in 

 very young cells. 



young cells, the protoplasm appears to fill the whole 

 cavity. It has a granular appearance, and these 

 granules are possibly either protoplasmic in nature 

 (microsomata) or food-particles, but the latter is 

 doubtful, as most food-materials exist in the cell in a 

 state of solution, except when they are in the form 

 of reserve-materials. 



These main features are seen if we make thin 

 longitudinal sections of the given tissue, which must be 

 stained (preferably with logwood), and properly 

 mounted either in Canada balsam or glycerine. 



There have l>een many assumptions made as to the 

 ultimate structure and chemical compiosition of proto- 

 plasm, amongst these being Nageli's miccllar theory 

 and the framework theory of Klein, Leydig, and others; 

 but the one that appears to account best for the various 

 physical properties of protoplasm is that due to 

 Biitschli, the foam or honeycomb theory, although even 

 to this there are objections. 



There seems to have been a tendency recently to 

 advocate this latter theory, on account of various sur- 



\Ve have (see Fig. i) an obvious cell-wall, and con- 

 tained within this the protoplasm; about the centre of 

 this latter is situated the nucleus, which is circular in 

 outline and in general shape spheroidal. In these very 



face-tension phenomena exhibited by emulsions, and 

 certainly the appearances presented by protoplasm are 

 in some cases very similar to these. But, whilst ad- 

 mitting the value of these observations, it is certain 

 that they do not wholly unravel the physical structure 

 of protoplasm. 



If we examine somewhat older cells, that is, cells 

 which have been carrying on their vital functions for 

 some little time, it will be seen that the protoplasm 

 no longer entirely fills the cell, but is thrown into 

 "bridles" or strands passing from a larger central 

 mass, which usually contains the nucleus, to the cell- 

 wall on all sides (see Fig. 2). The spaces not occupied 

 by protoplasm are usually filled with fluid, the cell-sap, 

 and this contains some of the nutrient materials for 

 the cell. The strands of protoplasm, as well as the 

 central portion, are still granular, and in some cases it 

 is possible to demonstrate fibrils passing between ad- 

 jacent cells, the so-called " intercommunicating fibrils " 

 (see I'ig. 3). These are well seen in the cells of the 

 young endosperm of Caltha palustris, and their im- 

 portance we shall enlarge upon later. A well-known 

 example of them exists in the communicating threads 



