586 



SCIENCE. 



[N. S. Vol. XII. No. .-^OS. 



lias arisen towards the conclusion of the 

 period of wood-forming activity." It was 

 found that in the broad-leaved trees ex- 

 amined no increase in thickness took 

 place until the buds had opened and 

 the first leaves expanded ; that the first 

 formation of new wood was in the neiglibor- 

 hood of the terminal bud ; that the first 

 growth was not continuous around the 

 stem, but of vessels and tracheids in ii-reg- 

 ular groups ; that the growth was continued 

 gradually from the one-year twig to the 

 two- and three-year twigs ; and that when 

 the new wood begins to form on five- and 

 six-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 grow^th 

 can be seen on the lower limbs. In the 

 pine an apparent exception was found, for 

 increase in thickness began on two- and 

 three-j'ear twigs before it began on one-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 twig for two or three years. In the hem- 

 lock, which holds its leaves for six or seven 

 years, the growth, when examined about 

 the end of May, was greatest on six- 

 year twigs and decreased up to the one-year 

 twigs where the growth was slight. On one 

 of the deciduous Gymnosperms, the bald 

 cypress (Taxodium distiehum), the condi- 

 tions seem to be as in the broad-leaved, de- 

 ciduous trees ; no growth in thickness begins 

 till the leaves are expanded, and then it be- 

 gins at the younger branches and extends 

 back to the older ones. 



On the Assimilation of some Organic Substances 

 by Plants : By J. F. Clark. 



Tlie Rheotropism of Roots: By F. C. New- 

 combe. 

 North American Sordariacea : By David 



Griffiths. 

 ITie Development of the Egg and Fertilization of 

 Finns Strobus : By Margaret C. Fergu- 

 son. 

 Nuclear Division in the Hepaticce : By B. M. 



Davis. 

 The History of the Bulbils of Lysimaehia ter- 



restris L. : By D. T. MaoDougal. 

 Observation on Root Flairs : By W. J. Beal. 

 The root hairs of Agrostemma Githago L. 

 and Lilene notifiora L. arise in vertical rows 

 of epidermal cells, and those of the former 

 are always extensions of the apical end, 

 while they arise in the middle of cells in 

 other species. Great variations in size and 

 form were found, and septate hairs were 

 seen on Chenopodium hybridum. Eoot 

 hairs are extremely sensitive to changes of 

 temperature and moisture. 



D. T. MacDougal, 



Secretary. 



THE FAITE OF SCIENCE* 



It has been said that, each man has one 

 thing to say, and that when he speaks twice 

 he repeats the second time what he said the 

 first. I hope that the saying is not wholly 

 true ; and yet I fear that in my case there 

 is a grain of truth in it. I was invited to 

 speak a year ago to the Graduates' Club, 

 and I suspect that I then said much that 

 I am always tempted to say to graduate 

 students. However, as your Dean has, for 

 lack of better available material, invited 

 me to address you at this your first meet- 

 ing of the year, I must say something ; 

 and so I shall take down again the old 

 fiddle, and give you what some of you will 

 recognize as merely a variation upon the 

 old tune. 



*An address before the Graduate School of the 

 University of Peunsylvania. 



