48 Dr. W. C. Williamson on 



the " points," a characteristic feature of the " Corona " of 

 these young twigs, are small and few in number. In the 

 section B, in the same slide, we have a similar condition. 

 The section of the primary cylinder has a diameter of 

 27 mm., whilst of the larger tracheids we have 308 and of 

 the smallest one 252. Thus in A we have a total of 681 

 and in B 560. But in the larger section, C.N. 1593, the 

 section of the Primary Xylem cylinder, which has a diameter 

 6'5 mm., contains 2910 tracheids, of which 11 10 are large 

 and 1800 are small and peripheral ; the latcer now prepon- 

 derating over the larger ones. In C.N. 380, which is from 

 my largest stem of this type, the diameter of the Primary 

 Xylem cylinder is 12 mm., but I can only count 2082 

 large tracheids. In the periphery, where the smaller 

 ones ought to be in considerable numbers, none are pre- 

 served. The numerous positions which they ought to 

 have occupied are clearly marked by a defined brown 

 tint, but the walls of the tracheids have entirely gone. 

 That these coloured areas mark points from which the 

 tracheids have disappeared, is demonstrated by another 

 specimen, from which most of the corona and its characteristic 

 " points " have vanished, their position being only repre- 

 sented by the brown stains referred to ; but in a small 

 portion of the circle these stains are covered by the 

 perfectly preserved small tracheids. In C.N. 381 all these 

 tracheids are exquisitely seen. The diameter of the primary 

 xylem is 9^5 mm. ; of the large tracheids there are 1572, 

 and of the small peripheral ones there are 2917. Whence 

 has the enormous increase in the older branches been 

 derived. The differences in the composition of the corona 

 in the younger and older branches is well shown in my 

 Memoir XIX. by the two figures 5 and 6. A comparison 

 of the above details will be seen at a glance in Table IV. 



Dichotomies — I have hitherto met with no example of 

 an equal dichotomy of the type of L. Harcourtii, but this 



