350 



THE AGRICTJLTUKAL NEWS. 



OCTOBEE 21, 1916. 



MElTHODS OF MEASURING GROWTH IN 

 THE SUGAR-CANE. 



It was suggested in the last issue of this Journal that 

 a useful purpose would be served if observations could be 

 made concerning the rate of growth of the sugar-cane. Such 

 observations would be valuable as an index of the effect of 

 weather change.s during the season's growth, and if carried 

 on systematically over a number of seasons, we might obtain 

 a clearer idea than is possessed at present, as to what is the 

 ideal sequence of weather conditions for high yields and 

 early maturity. From a practical point of view the observa- 

 tions would probably be of greatest use as a means of 

 comparing accurately the growth of different varieties; the 

 data might be expected to show to what extent weather 

 ■conditions determine differences in yield apart from soil 

 conditions and the constitutions of the different varieties. 



A rough idfa of the effect of weather changes can be 

 obtained by examining a .sugar-cane that is fully niatured. In 

 most cases it will be observed that the distances between the 

 nodes or joints are not uniform; two or three may 

 be close together, while at another point the length of 

 the internode may be above the average. These differences 

 are due to the effect of weather, principally rainfall. 

 Taking a cane that has been grown under comparatively 

 normal and uniform weather conditions, it should be 

 possible to deduce with a fair degree of accuracy what the 

 rate of growth has been. This can be done by dividing the 

 number of joints into the number of weeks during which 

 active growth has been in progress. Knowing the length of 

 a joint we are then able to express the rate of growth in 

 inches per week. 



The direct measurement of the rate of growth in the 

 sugar-cane is not an easy matter. Suggestions have been 

 made from time to time but they present difficulties when 

 attempts are made to put them into practice. The apical 

 growing region is inaccessible for measurement purposes. 

 The rate of growth in the different internodes varies from 

 a maximum rate in the apical bud to zero in the mature 

 internodes. It is not easy to decide, therefore, what method of 

 measurement to adopt, particularly for comparative purposes. 

 One possible line of procedure is in connexion with rate 

 of leaf development, or in other words, the rate of unfolding of 

 the terminal bud. It should be possible to note at specified 

 intervals of time the number of leaves that have unfolded, and 

 this would no doubt be found proportif)iial to the rate of 

 growth. To what extent the development of the leaf and its 

 period of functitmal activity is correlated with the develop- 

 ment of the internode towhicli it is attached, is not definitely 

 known. Probably the iiiternodc continues to grow after its 

 leaf has cea.sed to function. Very" few observations appear 

 to have been made. Nor has tlie question of the period of 

 functional activity of different leaves been enquired into. It 

 would be interesting to know how long different cane leaves 

 function. The period is probably dependent upon moisture 

 conditions. 



To come back to the main point of measuring cane 

 development, a method that possesses practical possibilities 

 is the following. Suppose one wishes to compare the rate of 

 growth in, .say, six different canes. Select in each ca.se a not 

 fully developed internode nearest to the surface of the soil, 

 in a very yraing plant or, say, 1 foot above the surface in an 

 older plant. Measure the distance ^between the two nodes by 

 means of a pair of dividers and record the measurement in 

 tabular form a< .shown above. In order to expose the 

 nodes, it will probably be found neces.sary to cut a slit 

 in the enveloping leaf sheath. Kopeat the observation 

 at, the end of ever^■ weel-. As well as the first internode 



just referred to, the one above together with all that may 

 be accessible may also be measured, and the figures recorded 

 in the same way. In subsequent weeks, as the cane grows, 

 still other internodes may be measured, and at the end of 

 two or three months a set of observations will have been 

 obtained and recorded after the manner indicated by a few 

 hypothetical cases .shown below. 



c o 



I— I c 



Weeks. 



10 



These results should show the rate of expansion of 

 the particular area under observation in each cane. They 

 would also indicate the'tirae when growth ceases in any one 

 node, and possibly bring out some of the adver.se effects of 

 unfavourable weather. 



It will be understood that the methods suggested are 

 only put forward tentatively with a view to their being tested 

 as to their practicability. Others will no doubt suggest 

 themselves to the plant observer interested in the matter. 



We may now turn from the stem growth to root growth. 

 To measure root growth in the cane plant is practically 

 impossible, but there are certain aspects of root development 

 that will allow of useful observations being mide. Varieties 

 differ in regard to the extent of their root system. 

 Presumably varieties characterized by having a large number 

 of canes to the stool and hence an extensive rhizome below 

 the soil, vrill have a wider root range than plants witli a few 

 canes to the stool. Varieties with extensive root system.s 

 may be expected to make unusually heavj' demands upon 

 the immediately available water-supply in the surface soil, 

 and such varieties might be expected to be susceptible to 

 even short periods of dry weather Actual observation shows 

 this to be the case in regard to the well-known variety 

 B.1753. As far as we know, there have been but few obser- 

 vations made in connexion with the relative root range in 

 dift'eient varieties. Tbe matter is important and should 

 receive the attention of tho.se engaged in experiments with 

 sugar-cane. 



In concluding, it ought to be more definitel}' stated, that 

 the principal object ifi'-'making the observations suggested 

 above is to determine as far as possible the influence of 

 weather conditions upon growth, and to find out to what 

 extent the constitution of certain varieties renders them lesS 

 susceptible than others. To achieve this end careful 



