THE LEAF-TRACE IN SOME PINNATE LEAVES. 
27 
Spiraea, lobata , Murray, 
A different type of leaf-trace is found in Spiraea lobata, Murray, S. Ulmaria, 
Linn., S. kamtschatica, Matsum., and Filipendula digitata { W.) Freyn, var. tomentosa 
(Led.) Freyn. In S. lobata, Murray, the leaf-trace is composed of separate strands, 
usually of five large and a varying number of smaller strands, arranged along the 
abaxial side of the petiole and rachis (text-fig. 17a). Below a pinna the large strand 
nearest to the margin of the series becomes horse-shoe-shaped and gives off the 
“ arch ” of the horse-shoe to the pinna, leaving the tips to re-form the leaf- trace strand 
(text-fig. 17&, c). This process is repeated in Spiraea Ulmaria and S. kamtschatica. 
In Filipendida digitata, var. tomentosa, the “ arching-up ” of the horse-shoe is more 
pronounced than in the other species. The method of supplying the greater portion 
of the pinna-trace in these species is very like the extramarginal method in the 
Text-fig. 17 . 
Ferns, but here the small strand actually at the margin of the series forming the 
leaf- trace passes out with the larger strand as the pinna-trace (text-fig. 1 7b, c). 
The species of Spiraea described above belong to three different Sections of the 
genus (Wenzig, ’88) — Spiraea Aruncus to the section Aruncus, Seringe; S. sorbi- 
folia and S. Lindleyana to the section Sorbaria, Seringe ; and S. Ulmaria, S. 
kamtschatiea, and S. lobata to the section Ulmaria, Monch. Focke (’94) raises these 
sections to generic rank, and separates Aruncus and Sorbaria somewhat widely from 
Ulmaria. But specific or even generic distinctions do not suffice to explain the 
differences in the leaf- traces described above. For in the genus Astilbe (which stands 
systematically further from Spiraea than do the genera Aruncus (Tourn.) Kostel and 
Sorbaria (Ser.) A. Br. from Ulmaria (Tourn.)) # the leaf-trace is exactly like that of 
S. Aruncus, and the pinna-traces are given off exactly as in that species and thus 
quite differently from the manner in S. lobata. 
The Leaf-Trace of Astilbe. 
In Astilbe rivularis, Ham., A. rubra, Hook. f. et Thoms., and in A. Thunbergii, 
Miq., the strands of the leaf- trace are rather less numerous than are those of Spiraea 
Aruncus, but they are arranged in precisely the same manner, though the distances 
between the adjacent strands are somewhat greater in Astilbe than in Spiraea. 
Text-fig. 16& represents exactly the method of formation of the pinna-traces in these 
species of Astilbe, the part of the ring of leaf-trace strands nearest to a pinna being 
extended towards the pinna and eventually nipped off as a pinna-trace. 
* Focke, loc . tit ., p. 12. 
