PKESIDEXTIAL ADDRESS. 893 



larg3 that it requires twenty-eight figures to express it, and placed end to end they 

 would stretch so far that a ray of light to travel from one end to the other would 

 take 100,000 years. The potentialities of protoplasmic catalysis are thus made 

 clear, but the actualities are speedily cut short by limiting factors. 



For a while, however, this ideal rate of growth is maintained. At the end 

 of every n minutes there is a doubled amount of protoplasm present, and this 

 will be capable of catalysing twice the amount of chemical change and carrying 

 on a doubled amount of growth and development. This is what common-sense 

 and the law of mass alike indicate, and is exactly what this logarithmic curve in 

 fig. 2 expresses. 



This increase of the amount of catalytic protoplasm by its own catalytic 

 activity is an interesting phenomenon. In Section K we call it growth, attribute 

 it to a specific power of protoplasm for assimilation (in the strict sense), and 

 leave it alone as a fundamental phenomenon, but are much concerned as to the 

 distribution of the new growth in innumerable specifically distinct forms. In 

 the Chemical Section they call this class of phenomenon ' autocatalysis,' and a 

 number of cases of it are known. In these a chemical reaction gives rise to tome 

 substance which happens to catalyse the particular reaction itself, so that it goes 

 on and on with ever-increasing velocity. Thus, we said that free acid was a 

 catalyst to the hydrolysis of cane-sugar ; suppose now that free acid were one of 

 the products of the hydrolysis of sugar, then the catalyst would continually in- 

 crease in amount in the test-tube, and the reaction would go faster and faster. 

 Under certain conditions this actually happens. Again, when methyl acetate is 

 hydrolysed we normally get methyl alcohol and free acetic acid. This free acid 

 acts as a catalyst to the hydrolysis, and the rate of change continually accelerates. 

 Here, if the supply of methyl acetate were kept up by constant additions, the 

 reaction would go faster and faster with a logarithmic acceleration, giving a curve 

 of velocity identical with fig. 2, A. 



For a clear manifestation of this autocatalytic increase in the plant it is, of 

 course, essential that the supply of food materials to the protoplasm be adequate. 



Another case where we might look for a simple form of this autocatalytic 

 increase in the rate of conversion of food materials to anabolites Avould be in the 

 growth of a filamentous alga, like Spirogyra. Here, as in the bacterium, all the 

 cells are still capable of growth. In this case the food-material needed in 

 greatest bulk is carbon, which has to be obtained by photosynthesis. Some 

 experiments have been started in the Cambridge Laboratory on the rate of growth 

 of Spirogyra in large tubs of water kept at different temperatures and with varying 

 facilities for photosynthesis and metabolism. Under rather depressing conditions 

 the Spirogyra took several days to double its weight — a rate of metabolism out of 

 all comparison slower than that of bacteria. Experiments on these lines, with 

 the difi'erent food materials as limiting factors, should give instructive results. 



We turn now to consider the growth of a flowering plant. Here conditions 

 are more complex, and we know that at the flowering stage or end of the season 

 the growth diminishes considerably. This dift'orence from a simple alga or 

 bacterium we can only regard as a secondary acquisition in relation to the 

 external conditions — either a reaction to a present external stimulus or to the 

 memory of past stimuli. In a flowering plant, too, all the cells do not continue 

 to grow ; many cells difierentiate and cease to grow and also some of the groups 

 of meristem remain dormant in axillary buds. Clearly the growth curve cannot 

 continue to accelerate logarithmically, and in later phases it must tail ofl'; the 

 ' grand period ' which growth is said to exhibit is another way of stating this. 

 It will, however, be of great interest to us to see what will be the form of the 

 curve of growth during the early period of development. 



The importance of this class of work has been realised in Geneva, and 

 detailed work is now being done under the inspiration of Professor Chodat ^ in 



' A. Monnier, Lcs matures minerales et la hi (Vaccroissemcnt des vegetavx, Geneva, 

 1905 ; N. Deleano, Le role et la fonction des sels mineravx dans la vie de la plantc, 

 Geneva, 1907. See also the independent work of Tribot, ComjJ'tes rendus de I'Acad, 

 des Sciences, October 14, 1907. 



