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CURRENT LITERATURE. 



Histology. 

 Harper, R. A. The structure of protoplasm. Am. Jour. Bot. G 

 (1919) pp. 273—300. 



A quarter of a century ago there was much speculation regarding the 

 physical structure of protoplasm. It was then expected that better fixation, 

 better staining processes, and more accurate microscopic observation would 

 reveal this structure. Since then there has been much evidence accumulated 

 bearing on the problem, though there has been little attempt to formulate 

 rigid theories of the structure of protoplasm. 



Professor Harper of Columbia University, in an address before the 

 Botanical Society of America in 1917, has brought to bear on the problem 

 what he considers to be the most important evidence from recent work in 

 cytology, in the chemistry of the colloidal state, and in genetics. He points 

 out that evolution has been along the lines of specialization of cells groups 

 and division of labour between cells, rather than by any change in funda- 

 mental cell organization. 



He considers that the most 'significant evidence from cytology is the re- 

 cognition of differentiated areas within the protoplasm, within which specific 

 processes are carried on. Examples -are elaioplasts or fat-forming bodies, 

 plastids of various kinds, vacuoles, and chromosomes. In many of the lower 

 plants the chloroplasts appear not to have-.a definite limiting membrane like 

 a plasma membrane, but are more or less vaguely restricted regions of the 

 protoplasm impregnated with chlorophyll. With increasing localization of 

 position and specialization in function, these protoplasmic areas finally be- 

 come permanent and self-perpetuating. Chromosomes, for instance, always 

 arise from pre-existing chromosomes by an astonishingly complicated and 

 precise division. He believes that " the bulk of the literature of the plant 

 chondriosome is a mere tabulation of the appearance of variously fixed and 

 colored particles in the cell body with the hope that such bodies may later 

 be found to be specific and fundamentally significant." The concept of 

 localized areas of protoplasm for specific function would include all the 

 organs of the cell, temporary as well as permanent. 



Perhaps the most important evidence from recent chemistry of the col- 

 loidal condition is the "recognition of the fact that the units of colloidal 

 systems, especially those of proteins, carbohydrates, etc., are large enough 

 to be distinguishable.at least with our present microscopes ". Protoplasm is 

 a colloidal substance, often thought of as a simple two-phase system with 

 water or some other non-living substance as one of the phases. Butschli 

 considered it to have an alveolar structure, with the living substance forming 

 the continuous walls and the non-living occupying the vacuoles; BEMERINCK 

 and others conceived of protoplasm as made up of granules of living sub- 

 stance distributed through a non-living matrix. Interpreted in terms of a 

 colloidal solution the first theory would make the continuous phase the more 

 important, while the second would make the disperse phase the more 



