March 21, 1902. J 



SCIENCE. 



455 



nal stimuli has been considered to be con- 

 fined to the apex and to the elongating zone. 

 The elongating zone in nearly all species is 

 confined to the first 10 mm. of the apex. In 

 studying the phenomena of rheotropism it 

 was found that the region of the root pos- 

 terior to the elongating zone is sensitive as 

 well as the elongating zone itself. To de- 

 termine the location of the sensory tissue, 

 various parts of the root were shielded 

 from the flow of the water by enclosure in 

 glass tubes. The roots of the radish, white 

 mustard, buckwheat, sunflower, and pop- 

 corn gave good rheotropie curves when 

 stimulated at a distance of 10 mm. to 15 

 mm. from the limit of the elongating zone. 



Francis Ramaley : ' Mesa Vegetation. ' 

 The plants of these long, gently sloping, 

 flat-topped ridges are distributed in char- 

 acteristic fashion, depending upon the vari- 

 ous edaphic conditions presented by differ- 

 ent slopes and exposures. Probably the 

 most interesting feature to be noted is the 

 distribution of trees and shrubs. These 

 plants are present on the tops of the mesas 

 at their western ends, absent farther east 

 because of dryness, present on the north 

 and absent on the south slopes. On the 

 south slopes shrubs occur near the top. 

 This portion of the slope, in most hills the 

 driest, is here somewhat moist because the 

 snow remains late in the spring on the flat 

 lops, and in melting the water trickles do^vn 

 the sides of the hill and is absorbed near the 

 top. There is thus more moisture near the 

 top than farther down, and the occurrence 

 of a fringe of shrubs and trees at the top is 

 thus explained. Illustrated by lantern 

 slides. 



D. M. Mottiee: 'The Behavior of the 

 Chromosomes in the Spore Mother Cells of 

 Higher Plants and the homology of the 

 Pollen and Embryo-sac Mother Cells. ' The 

 author discussed the behavior of the 

 chromosomes in the pollen mother cells of 



the species of Lilium, Podophyllum pelta- 

 tuin and Tradescantia Virginica, and in the 

 embryo-sac of Lilium Martagon, with the 

 following results: The earlier view of 

 Farmer and Strasburger, that a double 

 longitudinal division of the chromosomes 

 takes place during the first mitosis, is con- 

 firmed. The second longitudinal splitting 

 takes place in a plane at right angles to the 

 first. This is clearly seen during metaki- 

 nesis ; it may occur earlier. There is, there- 

 fore, no longitudinal fission of the chro- 

 matin spirem during the second mitosis, 

 and no reduction division in the sense of 

 Weismann. In the reconstruction of the 

 daughter nucleus the granddaughter chro- 

 mosomes unite to form a single chromatin 

 spirem. In Tradescantia especially, the 

 granddaughter segments tend to reticulate 

 so that an irregular spirem is the result, and 

 the daughter nucleus approaches the struc- 

 ture of the resting stage. The identity of 

 the individual chromosomes is lost in the 

 daughter nucleus. The first two mitoses in 

 the embryo-sac mother cell are like ia 

 character to those in the pollen mother cell, 

 and consequently the micro- and macro- 

 spore mother cells are homologous. The 

 type of development of the embryo-sac in 

 which the heterotypic and homotypic mi- 

 toses result in four potential macrospores, 

 as for example in Helleborus, is regarded 

 as the more primitive, while that found in 

 Lilium is considered as a derived form. 

 No case is known in which the pollcu 

 mother cell develops directly into the pol- 

 len spore. Illustrated by lantern slides. 



SECOND SESSION, 2 P.M. 



Meeting called to order by the chair- 

 man. About seventy-five were present. 

 The chairman read the following message : 

 Society of Plant Morphology and Physiology in 

 session at Columbia sends greetings to Botanists 

 of Central States at Chicago. 



Erwin F. Smith, President, 

 WnxiAM F. Ganong, Secretary. 



