37o 
Notes. 
mature the walls of the hypertrophied cells become brownish in colour and are 
slightly thickened, but do not show any trace of lignification. In none of the leaves 
examined were the outgrowths sufficiently large to prevent the proper working of the 
guard cells, though they occasionally came into contact with the auxiliary cells of 
the stomata. To determine the age of the leaf at which this occlusion commenced, 
leaves of all ages were sectioned, and it was found that, whilst there was no trace of 
abnormality in the young stages, the outgrowths began to develop as soon as the leaf 
was fully expanded and were complete in many cases within thirty days. A some- 
what parallel case is figured by Haberlandt 1 for Pilea elegans , in which, however, the 
occluding cell is much thickened and touches the guard cells. He also refers to 
similar cases in Camellia japonica and Prunus Laurocerasus. Krister 2 amplifies 
Haberlandt’ s statement and cites Molisch 3 as recording stomatal occlusion in Trades- 
cantia guianensis , T. pilosa , and T. zebrina. Haberlandt 4 also records the complete 
choking of the stomata of Tradescanlia viridis by the hypertrophy of the auxiliary 
cells. 
The plants of T. pulchella upon which the observations here recorded were 
made, were grown in a greenhouse which was not supplied with artificial heat, and in 
which, consequently, the temperature was only slightly higher than that obtaining 
outside. As this species is a native of Mexico it was thought that the low temperature 
had possibly had the effect of preventing adequate root absorption, and a number of 
experiments were performed with a view to testing the accuracy of this idea. In the 
first series an additional supply of water was given to a number of plants, which 
otherwise were under identical conditions with their fellows, and it was found that 
this treatment did not result in any noticeable diminution in the development of the 
swellings. In the second series a number of cuttings from the original plants were 
allowed to thoroughly establish themselves in a warmer plant-house, in which a con- 
stant temperature of 75°-8o° F. was maintained. They were liberally watered, and 
under these conditions very few cases of stomatal occlusion (four out of sixty 
examined) were found. Further investigation is, of course, necessary before the 
cause of these outgrowths can be regarded as settled, but the above observations were 
thought to be of sufficient interest to record. 
H. S. HOLDEN. 
University College, Nottingham. 
1 Haberlandt : Physiologische Pflanzenanatomie, 1909, p. 423. 
2 Kuster: Pathologische Pflanzenanatomie, 1903, pp. 106-7. 
3 Molisch : Ber. Senckenberg. Naturf. Ges., 1887, p. 117. 
4 Haberlandt: Ueber d. Bezieh. zw. Funktion u. Lage des Zellkerns bei d. Pflanz., 1887. 
