NATURAL SCIENCES OF PHILADELPHIA. 109 



May 2. 



The President, Dr. Ruschenberger, in the chair. 

 Thirty-four members present. 



Mr. Thomas Meehan exhibited some flowers of the 31agnoIia 

 jnijyurea, which were much curved toward the apex, and said tliat 

 this curvature was always towards the north when the flowers 

 opened in the full sun. This had alwaj's been a subject of specu- 

 lation witli him, as the tendency of growing vegetation was 

 usuall}^ towards the south, or towards the greatest source of light. 

 This season he has had the opportunity of examining man}- hun- 

 dred, and almost all were due north ; a few were either a little 

 west or east of north. The plants bearing these flowers were low, 

 and the sun had full power on all the opening blossoms. That 

 this northern tendency of the curve was, however, due to the sun, 

 was evident from the fact that when growing under the shade of 

 trees, the flowers of this plant were perpendicular, and of uniform 

 growth all round. 



This season he believed he had found the explanation. He ob- 

 served the same curving towards the north in the expanding male 

 catkins of Salix caprea. These, so long as elongation continued, 

 were perpendicular; when this ceased, the stamens developed first 

 on the warmest side, the side next the sun. The growth of these 

 expanding stamens was very rapid ; and he had observed that this 

 growth not only was towards the light, but the growing parts had 

 the power of drawing part of the axis to ivJiich itivas attached ivith 

 it. A ver}' small rise in the temperature was sufficient to excite 

 growth in the willow, and the diflerence between the sun striking 

 against the south side of the catkin, and the heat which could lie 

 commanded by the north side, made a diff"erence of several daj-s 

 in the expansion of the stamens on the respective sides. Some- 

 times a catkin would be formed on the north side of the plant, in 

 the shade of the tree, in which case the most heat cominir from 

 the north, that side of the catkin would expand its stamens first, 

 but slowly. In this case there would be a slight curve towards 

 the south. In the case of curved catkins, the curve was alwaj's 

 greatest after a hot burst of sun, when the stamens grew most 

 rapidly. When the northern side developed, the axis curved back 

 again, so that the ultimate direction was perpendicular, as it was 

 in the beoinnins:. 



The growth of the flower of magnolia being comparatively 

 slower, did not furnish the same evidence in detail ; but the results 

 were the same, and no doubt were influenced by the same law. The 

 flowers curved to the north while expanding ; but after a few da^'s 

 of full opening the north side caught up, and the flowers were 

 1871.] 



