57 [ 
Localization of the Sensitive Region. 
species having well-marked localization of light-sensitiveness 
seemed well suited for my purpose. My procedure is as 
follows : seedlings of Setaria , Sorghum , &c., are carefully 
removed from the sawdust in which they have germinated 
and placed immediately in water ; the best are then selected, 
the roots are cut off, and each seedling is fixed by pushing its 
cotyledon into a capillary glass tube, which is supported 
horizontally in damp air ; the seedlings are further supplied 
with water by means of a fine spray occasionally applied. 
They grow fairly well, but no doubt owing to the unnatural 
circumstances, they have not the full vigour and regular 
behaviour of properly rooted seedlings. A large number 
of experiments were made in this way, and though many 
cases occurred in which the seedlings either refused to grow 
or refused to geotrope, yet on the whole the result was 
abundantly convincing. 
The result was precisely what was expected on the hypo- 
thesis that the cotyledon is the sense-organ for gravitation. 
The free end continued to curve in one direction for days, 
producing a series of coils like a tendril, or even tying itself in 
knots. Three or four complete circles is the most I have seen ; 
but if the conditions were more favourable, I see no reason 
why more turns should not be made. The figures here given 
(Plate XXIX) are reproduced from accurate drawings kindly 
made for me by Miss Pertz while the experiments were in 
progress. The specimens were usually drawn when it was 
clear that growth, and therefore curvature, had ceased : they 
are not therefore any guide to the minimum time required 
for the production of spirals. In the figures the grains are 
shaded for the sake of distinctness ; the limit of the cotyledon 
is marked by a transverse line in Figs, i, 3, 4, 5 ( Sorghum and 
Setaria ) ; the cotyledon in Fig. 2 (. Phalaris ) extends to the 
grain. The roots were cut off to make the free end of the 
seedling lighter ; adventitious roots, however, often appear as 
shown on the hypocotyls in Figs. 3 and 4. Fig. 1 shows the 
simplest case of curvature, Fig. 3 the most complex. Fig. 1 
is interesting as showing that, when the cotyledon is only 
