18 TRANSACTIONS, NATURAL mSTORT SOCIETY OF GLASGOW. 



Experiments on the Thiekeningr of Some Tree Stems. 



By R. S. WisHART, M.A. 



[Read 23rd December, 1902.] 



It has long been known that the assimilated sap passes from 

 the leaves to where it is to be nsed or stored, through the 

 parenchyma and thin - walled bast tissue. That it descends 

 through the bast of the stem of a dicotyledonous tree has 

 often been demonstrated by removing a ring of this tissue 

 from right round the stem, and showing that by this the down- 

 ward current is checked. Where time and opportunity are 

 available, an experiment of this kind is most instructive, and 

 may well be recommended to all students or instructors in 

 what is now called " Nature Knowledge." The ways of accom- 

 plishing it may be various; but the best and surest way is 

 to cut out a ring right into the wood, and see that the wood is 

 scraped clean, so that none of the bast is left, and that the 

 cambium is also scraped out along with it. This is usually what 

 is recommended and done. But in some cases at least the 

 experiment may be performed in a simpler manner. In 

 November, 1897, I tied a branch of Sycamore tight with a 

 hard cord wound three times round about it, and waited for 

 future developments. As soon as the summer growth of the 

 following year began, the well-known bulging at the cord was 

 apparent. To begin with, there was a bulging below as well 

 as above, and this was my repeated experience, although we 

 usually hear only of the bulging above the cause of the inter- 

 ruption. My experiments, however, have most frequently been 

 worked upon branches and not upon main stems, and this might 

 account for supplies of assimilated food being to some extent 

 conveyed from below towards the point of interruption. In any 

 case temporary supply might have come from stored food. The 

 result was that, by the end of the first summer's growth, the 

 bulging above was not much greater than the bulging below. 

 This growth of the under portion was, however, only temporary. 



