The Spiral Disposition of the Leaves. 535 
of normal length, for instance of a decimeter or more, 
in the middle of a twisted stem. 
Like other anomalies spiral torsions are to a very 
large extent dependent on external conditions. Under 
unfavorable treatment the anomaly may be almost en- 
tirely absent, even from cultures from seeds which other- 
wise would give rise to a third or more of individuals 
with fine spiral torsions. The experiments which I have 
made on this point with Dipsacus sylvestris torsus and 
which have been confirmed by the results of my experi- 
ments with other species, seem to justify the following 
conclusion. 1 
The more favorable the conditions of life and the 
more vigorous therefore the growth, the greater will be 
the proportion of beautifully twisted plants in a given 
culture, and the more complete will be the torsions which 
are produced. 
The most important of these conditions is the space 
given to the individual plants. They ought not to be 
shaded by one another nor touch one another. More 
than 20-25 plants should never be grown on a square 
meter. Grown thus they nevertheless stand in close con- 
tact in autumn, and it is obviously still better that no 
more than 10-15 plants should occupy a square meter. 
Fewer torsions are produced on a given area when 
the plants are crowded than when the distances between 
them are greater. No useful purpose is therefore served 
by increasing the number of plants on the same bed. If 
nevertheless this is done the twisted individuals will be 
found almost exclusively along the edges of the bed. 
The time of sowing the seed is a point of considerable 
1 On Biastrepsis in Its Relation to Cultivation, Annals of Botany, 
Vol. XIII, 1899, p. 395- 
