924 REPORT—1899, 
MONDAY, SEPTEMBER 18. 
The following Papers were read :— 
1. On the Localisation of the Irritability in Geotropic Organs. 
By Francis Darwin, LBS. 
The seedlings of Setaria, Sorghum, and some other grasses are remarkable for 
possessing a hypocotyl or stalk-like part intercalated between the grain and the 
cotyledon. Rothert has shown that while the hypocotyl is the motor apparatus, 
the sensitiveness to light resides in the cotyledon, which transmits a stimulus to 
the hypocotyl, and this results in curvature. The author showed that the coty- 
ledon is also a sense organ for gravitation, the stimulus which leads to geotropic 
curvature being in like manner transmitted to the hypocotyl. If a seedling of 
Sorghum or Setaria is fixed by its grain to a support, so that the hypocotyl is hori- 
zontal, it bends apogeotropically till the cotyledon is vertical ; it then ceases to be 
geotropically stimulated, and no longer transmits an influence to the region of 
curvature, But if the conditions are reversed, if the seedling is supported by its 
cotyledon (which is fixed in a horizontal position), while the hypocotyl projects 
freely, the result is otherwise. The hypocotyl begins to curve upwards, just as in 
the first experiment, but it does not cease to curve when the free end points vertically 
upwards ; the curvature continues indefinitely, so that the hypocotyl curls into a 
spiral of three or four rings. This can only be explained by the assumption that 
the geotropic sensitiveness resides in the cotyledon, and that since the cotyledon 
remains horizonial it continues to be stimulated, and transmits a continuous 
influence to the motor part of the seedling, 
2. Studies in Aracee. By Prof. Douctas CAMPBELL. 
1. The Aracez have been much neglected in studies of the development of the 
flower and embryo, and our knowledge of these is very incomplete. 
2. The materials for the present studies were collected mostly in Jamaica, and 
include species of Dieffenbachia, Aglaonema, Philodendron, and Anthurium. A 
study was also made of Lystchiton, of Pacific North America. 
3. A study of the development of the ovule indicates that the primitive form is 
axial, as in other low monocotyledons. 
4, The early development of the embryo-sac follows the ordinary type. Later, 
there is a multiplication of the antipodal cells, and the sac becomes very early 
filled with endosperm. 
5. The ovule is often massive, and there is a marked development of mucilage- 
secreting hair upon the funiculus and the base of the nucellus. 
6. In all forms so far examined the embryo is destitute of a suspensor, and the 
cotyledon is very large, sometimes suggesting the scutellum of the grass-embryo. 
7. The forms with a single carpel are probably most primitive and most nearly 
related to the other low monocotyledons. 
3. Onthe Morphology and Life History of the Indo-Ceylonese Podostemacee. 
By J. C. Wiis, Director of the Royal Botanic Garden, Peradeniya, 
Ceylon. 
The paper read was an abstract of a forthcoming monograph of the Indian and 
Ceylon species of this very remarkable order of water plants, in which the various 
species will be described in detail, both morphologically and ecologically. A few 
typical species were described, their life history explained, showing the extra- 
ordinary modifications which the vegetative system has undergone to suit the 
needs of life in rising and falling water and in rapid currents. The vegetative 
organs consist largely of modified roots forming thallus-like bodies, and bearing 
