660 SUMMARY OF CURRENT RESEARCHES RELATING TO 



throughout the whole vegetation period. On the contrary, the large 

 conducting elements preponderate in the spring wood in deciduous 

 trees, corresponding with the rapid development of a large leaf area at 

 that season. Similarly the mechanical tissue is also very evenly dis- 

 tributed in the evergreen wood, forming generally the groundwork of 

 the wood. On the other hand, in deciduous trees the mechanical tissue 

 is formed mainly in the autumn wood when the need for conducting 

 tissue is lessened. 



Increase in Diameter of Trees.* — A. W. Borthwick has compared 

 results obtained by means of Pressler's increment-borer with those ob- 

 tained by actual measurements of circumference of trees extending over 

 a series of years. The experiments were carried out in the Royal 

 Botanic Gardens, Edinburgh. The results obtained by the two methods 

 closely coincided. By means of the increment-borer narrow cylinders 

 of wood can be extracted from the tree-trunk and the breadth of the 

 annual rings can then be measured. 



Abnormal Secondary Thickening 1 in Kendrickia.f — A. M. Clark 

 describes this process in K. Walkeri, a tropical climbing epiphyte be- 

 longing to the Melastoinaceae. The anatomy of the young stem is 

 typical of the family. At a fairly early stage numerous small patches 

 aud several large wedge-shaped areas of thin-walled unlignified wood- 

 parenchyma are cut off from the inner side of the completely circular 

 cambium ring. Later the cells at the central margin of the wedge 

 areas start new growth and cell-division ; the product of this growth 

 splits the axial woody ring into a varying number of portions. Later 

 on the quiescent cambium lying between the original internal phloem 

 and the axial woody ring resumes growth and proceeds to foi'm xylem 

 on the one side and phloem on the other. 



Pericycle of Angiosperms.J — J- Pitard has made extensive studies 

 on the evolution and the anatomic and taxonomic value of the pericycle 

 in this group. His communication is divided into five parts: — (1) His- 

 torical methods. (2) Evolution of the principal types of pericycle in 

 Angiosperms. (3) General phenomena of the evolution of the peri- 

 cyclic zone. (4) Taxonomic and anatomical value of the pericycle. 

 (5) Conclusions. As regards the evolution of the pericycle, the author 

 describes five methods by which the zone may follow the tangential 

 growth of the axis, viz. : — (a) By tangential increase in size of the cells 

 often followed by (/3) radial division of the cell, (y) Mem stretching, 

 a tangential increase accompanied by a radial decrease in diameter. 

 (8) Crushing ; the layer becoming flattened and killed by the centrifugal 

 pressure, (e) Rupture in the sclerenchyma when the zone is a ring of 

 sclerenchyma, as in heterogeneous pericycles where parenchyma alter- 

 nates with groups of sclerenchyma. 



Considerable variation in the radial diameter of the zone may occur 

 at different ages of the axis ; and the contour may also become altered 

 during the course of development. As regards function, the paren- 

 chymatous cells may contain chlorophyll and be assimilative ; later, 



* Report Brit. Ass.. 1001 (1902) p. 831. f Tom. cit, pp. 842-8. 



% Mem. de la Soc. des Sci. Bordeaux, ser. 6, i. (1901) pp. 173-360 (7 pis.). 



