The Plant World 



A MONTHLY JOURNAL OF POPULAR BOTANY. 



Vol. 111. AUGUST, 1900. No. 8. 



WHEN INCREASE IN THICKNESS BEGINS IN OUR TREES. 

 By Geo. T. Hastings. Presented By W. W. Rowlee. 



AS far as could be ascertained no special attention has been given 

 to the time when increase in thickness takes place in our trees. 

 One linds only such oeneral statements as this*: "The inner 

 portion of any one annual ring — is found in the spring; while the 

 outer portion — has arisen towards the conclusion of the period of wood 

 forming activity. ' ' 



Interest in the subject was aroused by the work of one of the 

 students (Miss Hopkins) in the laboratory at Cornell last year. Twigs 

 were gathered from several trees at weekly intervals through the 

 spring and preserved in alcohol and sectioned during the winter; the 

 object being to find when the cambial activity began. The results were 

 decidedly contradictory; one twig cut early in -May might show good 

 cambial growth, while another, cut a week later, might show none. 

 To account for these results it was sugo-ested that the growth migfht 

 ))egin at different times according to the location of the branch and the 

 distance of the piece sectioned from the terminal bud. 



To test this hypothesis six species of trees differing widely in 

 their structure were chosen. They were Acer ncgiindo^ Acer ruhruni^ 

 Plnus /StroJjifS, Quercii.s velutina^ Sal! x frag ills, and TtUa Americaiui. 

 Twigs were cut from these during April, May, and June; each time 

 selectino- the terminal shoot from a large branch, often also the termi- 

 nal shoot from one of the most vigoroiis u})per branches, and sections 

 made of the 1, '2 and 3 year old twigs, or a 5 or 6 year twig, and at 

 the same time a piece was cut from the trunk and sections matle from 



*Sachs, Physiology of Plants. 1887, p. 162. 



