54 The Ottawa Naturalist. [June 



MEETINGS OF THE BOTANICAL BRANCH. 



Held at the residence of Mr. D. A. Campbell, 226 Clemow 

 Avenue, Saturday evening, March 20th, 1909. There were 

 present in addition to the host, Messrs. Attwood, Whyte, Clarke, 

 Gibson, Michaud, Bond, and W. T. Macoun. 



The subject for the evening's discussion was "The Stems 

 of Seed Plants." Lantern slides, photographs and drawings of 

 sections of various stems were used to illustrate the types dis- 

 cussed. After a reference to the monocotyledon stem, a series 

 of slides was exhibited showing the various stages leading from 

 the soft herbaceous stem with relatively small wood bundles 

 to the woody stem with the wood bundle the major portion of 

 the stem. These furnished the material for the discussion. 

 Among the topics dealt with were growth in length and in 

 diameter, and the elements of the stem which contributed to 

 this growth, the chief active living portion of the stem being 

 the cambium, the medullary ray cells, the younger inner bast, 

 and the young outer wood. The function of each of these parts 

 of the tree stem was dealt with. The wood cells of the heart 

 of the tree gave stiffness, the wood cells of the sap wood were 

 the channels for water from root to leaf, the sieve tubes of the 

 bast carried food from leaf towards ro6t,the cambium was the 

 source of new cells added to wood and bast, the medullary rays 

 served to carrv water and plant food across the stem. 



In the discussion on sap flow and ascent of water in the 

 stem, some of the members were in doubt as to the existence 

 of such a force as root pressure and some were not prepared to 

 accept the proposition that living plant cells have the power 

 to select certain substances from the soil. It seems necessary 

 to assume a root pressure to account for the ascent of water 

 in a glass tube tied tightly a few inches above the soil to the 

 cut end of a stem. 



In reference to selective absorption it was pointed out that 

 two trees may grow in the same soil and one may contain more 

 ash than the other. Barley and red clover in flower grown in the 

 same soil have about the same total ash or mineral matter, yet 

 the clover contains over five times as much lime as the barley 

 and the barley about eighteen times as much silica as the 

 clover. 



Reference was made to a recent explanation of the ascent 

 of water in trees of great height. This explanation will be con- - 

 sidered more fully at some future time. It was generally con- 

 sidered that the known forces seem inadequate to fully account 

 for the phenomenon. ^- T:ii-^*^ 



