4 CELLULAR GROWTH. 



The growth of all such bodies — as it is of many others, but it is of 

 these I speak at present — is effected by the multiplication of the cells 

 of which they are composed. The process of cell growth and cell 

 production has been studied in numerous structures, both vegetable 

 and animal, with similar results ; and it may be described in general 

 terms thus : — In many cells, when examined microscopically, there 

 may be seen at one place a thickening of the cell wall ; in some may 

 be seen, in the cell contents, floating bodies, two, four, or more in 

 number, from which there is being developed a fine transparent 

 membrane, with an appearance like that presented by the glass on a 

 watch ; this gradually expands and is distended with liquid, until, in 

 process of time, the mother cell is ruptured by their distension, and 

 they continue to expand as independent cells, giving birth to others, 

 and in like manner giving place to these in their turn. 



It is not necessary to my present purpose that I should discuss the 

 question of how this process is originated and maintained. It is with 

 the process and what follows from it with which I have to do. To 

 prevent misapprehension, I may state that I do not know of the process 

 having been in any case observed continuously from its commence- 

 ment to its completion ; but different cells have been seen and studied 

 In all the stages of growth and reproduction to which I have referred. 



The increase of bulk in each cell may be too minute and too slow to 

 be noted, but with the process going on simultaneously in a long line 

 of cells the effect may be perceived. I have seen the extremity of a 

 conferva, held fast at the other end, advance across the field of vision 

 in a microscope with which I was examining it. Nor will this be 

 astounding if it be considered with what rapidity the process of cell 

 production, growth, and reproduction must sometimes go on. Large 

 tracts of snow in Arctic regions, and in Alpine districts, are some- 

 times quite suddenly reddened by the production of the Red Snow 

 plant, to which reference has been made, the consequence of the 

 development of innumerable cells. One form of fungus, the Phallus 

 impudiens, has been observed to shoot up three inches in the space 

 of twenty-five minutes. Another, Bovista Gigantea, the giant puffball, 

 " has grown," says Balfour, "in a single night in damp weather from 

 the size of a mere point to that of an enormous gourd. From an 

 approximate calculation it is found that in this plant not less than 

 20,000 new cells are formed every minute. Kieser estimated that 

 the tissue of some fungi augmented at the rate of 60,000 cells 

 per minute." 



In South Africa I have frequently observed a marked difference in 



