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SCIENCE PROGRESS 



stem bearing them, at least in conifers. Meissner proved this 

 in the case of Pinus sylvestris and Picea excelsa, and from his 

 results obtained in reference to the former I have roughly 

 calculated the percentage share of the whole growth in length 

 of the year's stem and the needles supplied in months of the 

 growing season. The statistics are given in the succeeding 

 table, which also contains the corresponding particulars as to 

 growth in thickness at approximately the same time, as 

 measured by Mischke, whose work is described later in this 

 article. (The dates in brackets are Mischke's, the others are 

 Meissner's.) 



Percentage of Growth of Pinus sylvestris during Successive 

 Portions of the Growing Season 



In two of the shoots of the Scots Pine examined by Meissner 

 the stem had attained by the end of June 98 and 99 per cent, 

 of its full length, whereas the leaves had attained only 60 per 

 cent. In a third shoot the percentages of the full growth for 

 the stem were 92 before the middle of June, almost 99 at the 

 end of June, while the corresponding percentages for the leaves 

 were 34 and 60. Thus in Pinus sylvestris the leaves lag behind 

 the stem as regards growth in length. Meissner observes that 

 the reverse is the case in Picea and Abies, whose leaves are 

 more forward in development than the stem. 



Questions concerning the periodicity of growth in thickness 

 of woody stems and roots have been investigated by methods 

 of two different types. The microscopical method of observing 

 the behaviour of the cambium to determine the dates of com- 

 mencement and conclusion of its activity was used by von 

 Mohl, T. and R. Hartig, Russow, Mer, Gulbe and Strasburger ; 

 it was utilised by R. Hartig to determine the fractional parts 

 of the annual ring produced during the successive portions of 

 the growing season. Mischke used the very delicate method 

 of counting the number of tracheids in the same annual ring 



