On the Secondary Tissues in Certain Mono- 
cotyledons. 
BY 
D. H. SCOTT, M.A., Ph.D., F.L.S., 
Honorary Keeper of the Jodrell Laboratory , Royal Gardens , Kew , and late 
Assistant Professor in Botany , Royal College of Science, London . 
AND 
GEORGE BREBNER, 
late Marshall Scholar in Biological Research, Royal College of Science, London. 
With Plates III, IV, and V. 
T HE present paper treats of three distinct questions, re- 
lating to the general subject indicated by the title : — 
i. The development of the secondary tracheides in Yucca 
and Dracaena. 
2 . The secondary growth in thickness of the roots of 
Dracaena. 
3. The secondary growth in thickness of Aristea corymbosa , 
Benth. (N. O. Irideae). 
No prefatory remarks to the whole paper are necessary, as 
a general knowledge of the monocotyledonous type of cambial 
growth is assumed. 
1. The Development of the Secondary Tracheides 
in Yucca and Dracaena. 
For the last seven years a controversy has been carried 
on as to the nature of the water-conducting elements in the 
secondary wood of Dracaena , and other Monocotyledons with 
a similar mode of growth. Up to 1886 it had been generally 
[Annals of Botany, Vol. VII. No. XXV. March, 1893.] 
