

1901] GEOTROPISM OF STEMS 419 
of alteration or reversal of irritability during the development of 
plants or their parts, independent of any changes in external 
conditions. At first sight the young hypocotyl of Lupinus 
seemed to present such a case, but investigation shows that 
there is no change in the nature of the perception in any 
esthetic tract, but merely change in the zone controlled. Very 
possibly, renewed study of some other cases, such as the erect 
tip of runners, or the tips of many climbers—at first seemingly 
positively heliotropic, but later appressed to the support —will 
show that no esthetic center undergoes any essential change; but 
rather that different parts of the growing region are under differ- 
ent control, or that the development of new members introduces 
automatic curvatures (nastie), or that the tendency to symmetry 
(autotropism, rectipetality) eliminates curves in parts which 
grow out of the zone of influence of an esthetic center. Nuta- 
tions too suggest themselves here. 
Most intimately related to the positive geotropism of the 
hypocotyl is that of the cotyledons of numerous monocotyle- 
dons, serving at the apex as organs of absorption in the endo- 
sperm, but elongating at the base and carrying the remainder of 
the embryo out of the seed. These have long been known to be 
positively geotropic.%* I have made the same experiments on these 
as on Lupinus, and so far as the initial downward curve is con- 
cerned with strictly analogous results. Several seeds were 
tried, of which Phoenix and Yucca angustifolia were found most 
suitable subjects. 
The growing region of Phoenix is rather long, though elonga- 
tion is considerable throughout most of it. The root begins to 
develop after the elongation of the cotyledon is about complete. 
The first table of results is from six plants of very different size, 
on four of which the root was still only a rudiment. The 
*©SacHs: Ueber die Keimung des Samens von Allium Cepa. Gesamml. Abh. 
oe from Bot. Zeit. February 1862. 
NK: Lehrbuch 1: 465. 
—. isa paper, which I know only by a very brief notice in Bot. Jahresb. 
15 : 622, by ee Spa: (Bidrag till hjertbladets anatomi hos Monocotyledonerna, in Sv. 
V. Ak. Bih, III. 12: —~. 1887), giving a list of plants with such cotyledons. 
