EXPOSURE ON LENGTH AND BREADTH OF LEAVES. 381 
ratio of 2°65. Both show a greater ratio for the plants grown in 
wet air. Both Dufour and Sorauer measured the lengths of but 
very few leaves. Those in Dufour’s experiments, e.g., are the 
actual lengths and breadths of individual leaves. My own results 
are all averages, and it is, I think, easier in this way to get rid 
of individual variations. 
MM. Vesque and Viet also give a few measurements from 
their culture experiments. 
When the plants (spinach) were grown in lines 25 em. apart, 
1 : 
When entirely isolated this was = u ora ratio of 1'92. This 
the ratio 
shows exactly the same influence. 
Wiesner, in his ‘ Biologie d. Pflanzen,’ pt. iii. p. 51, has also 
figured a very striking case of extraordinary elongation due to 
growth in humid conditions, and caused, as he suggests, by the 
greater * ductility " of the leaf under these circumstances. 
Costantin (Ann. Sei. Nat., Bot. ser. 7, vol. iii. 1886) also 
speaks of “ un allongement exagéré parallèlement aux nervures ” 
in plants grown in humid conditions (milieu aquatique). 
This summer I had a small experimental garden formed for 
the purpose of trying the effect of different soils on the growth 
of annuals. The garden consisted of five beds, only one foot 
apart from one another, and consisting respectively of:— 
lst. Peat (24 feet deep). 
2nd. Caleareous sand and loam, 
3rd. Pure sand. 
4th. Leaf-mould and sandy loam. 
5th. Manure and sandy loam. 
The plants were sown across all these beds. 
The following Table (p. 382) shows the result of the measure- 
ments of the leaves, 100 from each bed having been measured 
in almost every case. 
These results show that the leaf-ratio, instead of being in the 
order of the actual length of the leaves, that is, shortest in the 
peat and gradually longer in sand, lime, manure, and leaf-mould 
respectively, follows almost exactly the reverse order, being 
highest in the case of the sand-plants, and lowest in those of the 
manure. The heights of the plants in the various beds were 
in the same order as their length of leaf ; that is, the peat-plants 
