THe JOURNAIs 



OP 



Yfie department of Hgricufture 



OF 



V I CTO R I A . t^oTxr^K^^^L 



Vol. VIII. Part 6. 10th June, 1910. 



LIMITING FACTORS IN AGRICULTURE. 



Alfred J. Ewart, D.Sc. Ph.D., b'.L.S., Government Brtan'nt, and 

 Professor of Botany in the Melbourne University. 



Wherever and whenever the co-operation of several factors is necessary 

 to produce a given result, the non-fulfilment of any one of them invalidates 

 the remainder. For instance, to build a modern steam-ship, various kinds 

 of skilled work are necessarv, and the different workers are not inter- 

 changeable, so that the absence of anv one set of workers may th.row all 

 the others idle and prevent them from w-orking on, or from completing the 

 ship. In the same way, the rate at which a house can be built primarily 

 depends upon the rate at which the walls are constructed, and no number 

 of painters, finishers or decorators can hasten the construction of the 

 house, until the first factor, the building of the walls, is fulfilled. 



In the ca.se of plants, the factors essential to^ its life all act, for the 

 most part, throughout their whole existence, instead of successively as to 

 some extent they do in the instances quoted above. Hence, any essential 

 factor or condition which is not fully satisfied, reduces the possible action 

 of the others to the same level, or renders them useless if it is not fulfilled 

 at all. 



The factors essential for the growth of a green plant are — 



1. A supply of water. 



2. A certain temperature. 



3. A supply of air, containing oxygen and a trace of ca.rlxjn dioxide. 



4. Exposure of its leaves to light. 



5. A supply of mineral salts derived from the soil or elsew-here. 



Under ordinary circumstances, particularly in the case of plants which 

 staxt from large seeds, these factors are of importance in the order named. 

 That this is so is shown by the following facts. A pea or bean, or indeed, 

 any large .seed, can be grown to a considerable size and will develop a root 

 sy.stem, as w^ell as a stem and leaves, if supplied with water and kept in 

 moderately warm air. In this case, factors i and 2 are satisfied and 

 5997. N 



