Blackman . — The Compound Interest Law and Plant Growth. 359 
The fall in efficiency after the first few weeks of growth may perhaps 
be correlated with the mechanical relations connected with larger size. A 
doubling of the leaf area would require a stem of more than twice the 
weight to attain equal strength. Gregory 1 found that with larger leaf areas 
the ratio of stem weight to leaf weight went up. 
As the efficiency of the plant is highest in its early stages favourable 
conditions at that time should have a marked effect on growth. If a plant, 
owing to such conditions, should double its size as compared with another 
plant, then there is no reason why that advantage should not be retained to 
the end of the growing season. A ; good start ’ means, among other things, 
a larger capital to work with throughout the growing season. 
Gericke, 2 investigating the effect of various injuries on the growth of 
Helianthus animus , showed that the removal of the cotyledons not only 
affected the total weight — -as was to be expected, since a large portion of 
the plant’s capital was thereby lost — but also markedly reduced the 
efficiency of the plant. Calculations from his weekly data of dry weights 
show that the efficiency index never rose above 14-24 per cent, per day as 
compared with the 18-46 per cent, of normal plants. It is not at all clear 
why the loss of the cotyledons should reduce the economy of working of 
the plant developed from the remaining portion, especially as the removal 
of one cotyledon and one of the first leaves had no such effect. It suggests 
that the cotyledons may contain a supply of some special material necessary 
for the proper development and efficiency of the plant ; a possible analogy 
with the growth substances of animals occurs to one. The subject certainly 
requires further investigation. 
Kiltz (loc. cit .) observed in Nicotiana a marked decrease in dry weight 
at the time when the seed was matured, reaching 2-98 per cent, in the case 
of N. gigantea. This might be explained by assimilation being brought to 
a standstill while respiration continued. The amount to be explained in 
this way is, however, very large, and Chodat, Monnier and Deleano 3 have 
described a restoration to the soil of mineral matter up to 40 per cent, of the 
dry weight of the mature plant. Whatever its cause, the phenomenon is of 
importance in all experiments where the dry weight of annual plants which 
have reached the fruiting stage is in question. 
Summary. 
Attention is drawn to the fact that the growth of an annual plant, 
at least in its early stages, follows approximately the ‘ compound interest 
law ’. The dry weight attained by such a plant at the end of any period 
will depend on (1) the weight of the seed (or the seedling at its start), 
1 Experimental and Research Station, Cheshunt, Herts., Report III, p. 24, 1917. 
2 F. Gericke : Experimented Beitrage zur Wachstumsgeschichte von Helianthzts cmnuus. 
Inaug. Diss., Halle, 1-43, 1909. 
3 Bull, de l’Herbier Boissier, vii. 350 and 948, 1907. 
