Intumescences on the Leaves of Marlea 
begoniifolia, Roxb. 
LAST summer my attention was drawn to the peculiar appearance 
presented by the leaves of a plant of Marlea begoniifolia growing 
under glass in the Royal Botanic Garden. On closer examina- 
tion it was seen that the under surfaces of the leaves were studded 
with minute outgrowths, the largest barely exceeding I mm. in 
height. They varied in colour from the yellowish-green of the 
smaller swellings to the dark brown of the larger protuberances. 
They were absent from the upper surface, and were not observed 
on the other vegetative organs of the plant. 
Microscopic examination of these structures showed that each 
had its origin immediately below a stoma. Division of the 
underlying cells of the mesophyll, accompanied by longitudinal 
division of the epidermal cells around the stoma, resulted in the 
formation of a hemispherical swelling, composed of thin-walled 
cells with vacuolated protoplasm and prominent nuclei, and 
enclosed by the extended epidermis, the stoma now being 
situated at the apex of the outgrowth, and completely occluded 
by the underlying compact tissue derived from the repeated 
division of the mesophyll elements. It is worth noting that 
although stomata are also present in the upper epidermis of the 
leaf, yet there was no hypertrophy of the tissues on that surface. 
As the outgrowths increase in size they become lobed or 
branched, while the included elements are much elongated, with 
sparse protoplasmic contents and large vacuoles. At this stage 
the encompassing epidermal layer appears to have become 
disorganised, and the outline of each malformation is extremely 
irregular. Ultimately the outgrowths wither and die. 
Intumescences resembling those found on Marlea have been 
recorded by Tomaschek * as occurring on Ampelopsis hederacea, 
while similar outgrowths in various plants have been described 
by Frank + and Sorauer.t More recently Miss Dale § has in- 
vestigated very fully the nature and cause of the intumescences 
on Hibiscus vitifolius, and her conclusions as to the conditions 
favouring the production of the malformations suggest that the 
abnormal structures on the leaves of Marlea owe their origin to 
similar environmental conditions. A moist atmosphere, pro- 
vided there is a sufficient temperature, seems to create a patho- 
logical condition inducing the formation of these outgrowths in 
Mariea as in Hibiscus ; but, so far as is known, there has been 
no previous record of their occurrence in the former genus. 
M. Y 
* A, Tomaschek in Oester. Bot. Zeitschrift, xxix (1879), p. 87. 
; A. B. Frank, Krankheiten der Pflanzen, iii (1896), Pp. ae 
t P. Sorauer in Ber. Deut. Bot. Gesell., xvii (1899), p. 4 
§ E. Dale in Proc. ¢ . Phil. Soc., x( 1899), p. 192, ae in Phil. Trans. 
Roy. Soc., Ser. B, cxciv ¥ (908), A 163. 
[Notes, RBG. ., Edin., No. January 1021.1] 
