Oct. 1, 1919 Notes on the Composition of the Sorghum Plant 5 



decrease of the fiber is the same as the percentage of increase of the 

 soluble carbohydrates. The percentages of crude protein, ash, and ether 

 extract remain practically the same throughout growth. 



When these percentages are computed to the absolute weight of each 

 constituent in one plant, the same facts, with but slight modification, are 

 apparent. Figure 2 presents these data. The actual weights of pro- 

 tein, fat, and ash in each plant increase but slightly during the periods 

 of growth studied; the fiber about doubles in weight, while the nitrogen- 

 free extract trebles in weight. The stages of development studied here 

 represent not only maturation of the plant but actual growth, the height 

 increasing by 2 or 3 feet during these stages. It is apparent that the 

 plant absorbs practically all of its mineral requirements, including 

 nitrogen, during the early stages of growth, that it also lays down the 

 necessary structures of protein and fiber during these stages, and that 

 during the final maturation periods all the energies of the plant are 

 directed toward the filling out of the seed and the storing of sugar in the 

 cells of the cane. This program of development may prove to be the 

 rule in all plants, as it has already been proved in several of them, notably 

 in wheat, by Thatcher (16). 



The sharp decline in the curves in figure 2 for the last growth period 

 is explained by the fact that the plots had been culled of the larger plants 

 and smaller plants had to be chosen for the final stage. Thus the per- 

 centage curves continue in the direction anticipated, while the curves of 

 absolute weights show a declination. 



The above observations concern the whole plant. Considering now 

 the separate parts of the plant, it is found on examination of figure 3 

 that the leaves undergo changes in composition which are in many ways 

 similar to those of the whole plant. The nitrogen-free extract exhibits 

 a marked increase during the later stages. This is not paralleled by an 

 equal decrease of fiber, however, as was the case with the whole plant. 

 The fiber remains constant, both relatively and absolutely (fig. 4). The 

 percentage of protein undergoes an appreciable decrease, while the abso- 

 lute weight of it remains practically constant. The changes in dry 

 matter are closely parallel to those of the nitrogen-free extract. This is 

 corroborated by Collier's analyses of the juice of leaves (5, p. 142), which 

 showed a considerable increase of sugars in the more mature stages. 

 These data would indicate that the more mature the leaves the higher 

 their feeding value. 



Figures 5 and 6 present the curs^es for the composition of the tops. 

 In the preparation of the samples the cane was cut off just below the 

 lowest stem of the seed head, and the whole head used in the analyses. 

 This of course resulted in the earlier samples' consisting mostly of stems, 

 hence the high fiber content. Later, due to the filling out of the seeds 

 with starch, the percentage of fiber underwent a marked decrease, while 



