114 THE PLANT WORLD. 



it. Most' of the sections were stained with h^ematoxylon, but the best 

 results were obtained by staining lirst with methyl blue, washing and 

 staining lightly with hc^matoxylon; by this means the wood wath thick- 

 ened, lignilied cell walls took a clear blue color, while the newly- 

 formed, unlignified cells took a lavender color. 



It was found that in the broad-leaved trees examined no increase in 

 thickness took place until the buds had opened and the first leaves ex- 

 panded; that the first formation of new wood was in the neighborhood of 

 the terminal bud; that the first growth was not continuous around the 

 stem, but of vessels and tracheids in irregular groups; that the growth 

 was continued gradually from the 1 year twig to the 2 and 3 year 

 twigs; and that when the new wood begins to form on 5 and 6 year 

 twigs the process becomes very rapid, seeming as if at that time 

 growth began simultaneously over the whole tree. Growth usually 

 begins and extends more rapidly on the upper more exposed limbs, 

 sometimes a week before any sign of growth can be seen on the lower 

 limbs. 



In the Pine an apparent exception was found, for increase in 

 thickness began on 2 and 3 year twigs before it had begun on 1 year 

 twigs and before the buds had opened. By the time the buds were 

 well opened the growth had extended from the terminal shoot down 

 the trunk and growth was just beginning on the lower branches. 

 This seems to be due to the leaves remaining on the twiir for 2 or 3 

 years, the growth begins earlier and a little back from the terminal 

 bud and from there extends down the trunk as in other trees. In ihe 

 Hemlock, which holds its leaves for 6 or 7 3'ears, the growth, when ex- 

 amined about the end of May, was greatest on 6 year twigs and de- 

 creased up to the 1 year twigs where the growth was slight. On one of 

 the deciduous Gymnosperms, the Bald Cypress {Taxodlum distichum)^ 

 the conditions seem to be as in the broad-leaved, deciduous trees; no 

 growth in thickness begins till the leaves are expanded and then it 

 begins at the younger branches and extends back to the older ones. 



From the few observations made upon roots it seems probable 

 that increase in thickness begins later than in stems and takes place 

 more uniformity, though as in the stems it begins at the tips. 



That the cambium is active before new wood begins to form is 

 •hown by the leadiness with which the bark peals. 



With the Willow the buds were opening on April 23 but no 

 growth had occurred. Two weeks later, May 8, the buds were well 



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