THE PLANT WORLD. 115 



opened and the catkins in flower; growth was well started on the 1 

 year twigs and a ring of wood mostly of 1 layer of vessels thick was 

 formed over the whole twig but no increase had begun on the 2 year 

 twigs. On May 1-1, growth had extended to the 2 year twigs and the 

 wood on the 1 year twigs was 2 or 3 vessels thick. 



On ISIay 22, growth was well advanced on the 1 and 2 year twigs, 

 about 2 vessels thick on the 3 year and just beginning on the trunk, 

 where a few thin-walled cells had been cut off by the cambium. On 

 the root slight growth had taken place on 1 and 2 year rootlets but 

 older ones showed none. On June 2, the growth on the trunk was 

 considerably greater but none of the cell walls were thickened, and 

 the older roots showed slight amounts of new wood. On June 15, 

 when the twigs seemed to have nearly reached their full length by 

 comparison with the lengths attained in previous years and by the 

 number of leaves borne, the first elements formed on the trunk had 

 thickened lignitied walls. 



With the Box Elder the buds were opening on April 30, and new 

 wood was forming within 5 or 6 mm. of the terminal bud. On April 

 30, the buds were well opened and the first tow leaves expanded, 

 and at this time the growth is continuous around the stem for 15 cm. 

 below the bud; farther down the growth is irregular and on 2 

 year twigs none has occurred. On May T, the growth had extended 

 over the 2 vear old twigs and was beoinnino- to form on the 3 year old 

 twigs. On May 31, traces of new growth could be seen on the trunk, 

 and on June 12 the new wood on the trunk was thicker than on the 

 twigs; on the 15th the twigs had nearly reached their full leangth and 

 the new wood on the trunk was nearly all lignified. 



With the Red Maple the flower buds were fully opened and the 

 leaf buds beginning to open on April 21:th, but no new wood had been 

 formed. On May 10th, two pairs of tiny leaves had expanded, and 

 traces of new wood were found within 2 mm. of the bud. On May 29, 

 a ring of wood of a layer of vessels has been formed over the 1 year 

 twig, and growth had begun on the upper parts of the 2 yejir, while 

 not till the middle of June was growth evident on the trunk, and then 

 no new wood had been formed on the older roots and very little on the 

 young roots. 



\Vith the Basswood the l)uds did not open till the first week in 

 May, but the progress in wood formation was the same as in the other 

 cases. 



