870 Yapp. — Spiraea Ulmaria and Xeromorpky in Marsh Plants . 
EXPLANATION OF PLATES LXXXI-LXXXIII. 
Illustrating Professor Yapp’s paper on Spiraea Ulmaria , L. 
The plates consist of photographs taken from dried and pressed leaves of Spiraea Ulmaria , L., 
to illustrate the distribution of hairiness. In each case, only the lower surface of the leaf is shown. 
Hairy parts are white, glabrous parts dark. 
PLATE LXXXI. 
Shows all the leaves formed during one season on an erect flowering shoot. The leaves are 
arranged and numbered in order of development. Leaves 1-7 are radical, and 8-16 cauline. There 
is (as always) a gradual transition from glabrous to hairy leaves. The shoot was grown under fully 
insolated conditions. Note the narrowing of the leaflets in the upper leaves (cf. Text-fig. 5). 
PLATE LXXXII. 
A selected series of radical leaves. N.B. These were taken from a number of different non- 
flowering shoots. This series is arranged to illustrate the distribution of hairiness on partially hairy 
leaves. Note the increase in hairiness of successive leaflets as the individual leaf is ascended : the 
terminal leaflet is invariably the most hairy. Compare the increase in hairiness of successive leaves 
as the entire plant (flowering shoot) is ascended — see PI. LXXXI. In individual partially hairy 
leaflets the hairs usually form a marginal band, with sometimes (e. g. Nos. 4, 6, and 9) extensions in 
the form of bands between the main veins (cf. the localization of exposure withering — Text-fig. n). 
PLATE LXXXIII. 
Three partially hairy leaves. No. 1 shows the marginal bands of hair; No. 3 the additional 
interveinal bands. The terminal leaflet of No. 2 illustrates a not infrequent case in which only the 
innermost portions of the interveinal bands are developed. These now show, in addition to the 
marginal bands, patches of hairs occupying the forks of the veins. 
