C. A. EARBKR 73 



surface of the soil. A similar contrivance has been aliown to exist in certain 

 young sugarcane seedlings (p. 47), but observations have not been recorded as 

 to this habit in deeply planted sugarcane sets. In our dissections, however, we 

 not infrequently meet with what might be termed upright runners, in which, 

 long, thin internodes are intercalated between the usual, congested short 

 internodes of the base, and doubtless the meaning of this is sometimes the 

 same as that in seedlings, in that thereby the underground part may be placed 

 in the best position for rapid branching, near the soil surface. Tillering cannot 

 take place satisfactorily unless the shoots are able immediately to emerge 

 into the light. But when a certain number of branches have been developed, 

 and the light space so to speak is filled, further shoots are at a disadvantage 

 in that they are overshadowed by their neighbours. This is undoubtedly 

 the cause of the great mortality in cane shoots during the growth of the crop, 

 and it is not easy to see how this perfectly natural eSort at producing as many 

 branches as possible can be prevented, if the plant itself has not the power to 

 adapt itself to the conditions. It is fairly certain that this death of shoots is 

 not due to the lack of food supj)ly in the soil, for this can be and, habitually, 

 is supplied to meet all possible needs. Generally speaking, all plants in 

 the light branch more freely than in the shade. Growth in length is 

 repressed in light and a more spreading habit is induced which gives 

 room for more shoots to be developed. As one author has justly argued, 

 of all the food producers on which the plant is dependent, light is the 

 only one over which we have no control. There is a definite amount 

 of light available for each area, and this we cannot increase bv any means, 

 whereas air is moving, and water and salts can be applied artificially. "We 

 can increase the depth of soil and the amount of water, can improve the physi- 

 cal condition of the soil and add manures as desired, but, as soon as the amount 

 of light available is fully occupied, the further branches are shadowed and 

 unhealthy, however many we may by various means cause to be developed. 

 It is a common experience that trees on the outside of a forest, or in free space, 

 are much larger and more uniformly developed than those within the forest, 

 and this is not only due to their greater command of the soil around but also 

 to the light available, and the same applies to cane plants near the edges of 

 the fields or along the sides of the paths. The problem of obtaining the 

 greatest number of canes per acre is thus seen to be strictly limited by this 

 factor, as well as by those of cultivation and manuring. Light is perhaps the 

 most important limiting factor as regards tillering. 



Moisture also undoubtedly affects tillering, as can be seen by studying 

 the plants along the irrigation channels where they are as closely planted as 



