Problem of Xeromorphy in Marsh Plants . 8 1 7 
World forms, with pinnate leaves and exactly the same type of pubescence, 
i. e. their leaves are ‘ subtus albo-tomentosa \ The second group includes 
several N. American species with entire leaves, belonging to the § Euspiraea . 
Their pubescence is more or less similar to that of the first-named species, 1 
e. g. vS. Douglasii , Hook., wS. tomentosa , L., &c. 
It is interesting to note that most of these densely pubescent species 
have closely allied glabrous forms. Thus S. Ulmaria has the nearly 
glabrous variety denudata ; 2 5. palmata has the varieties tomentosa and 
glabra ; and 5. vestita is practically indistinguishable, except in respect of 
hairiness, from the glabrous K amtschatica, Pallas. Again, the two 
N. American species mentioned above are allied not only to each other, but 
also to the widely distributed glabrous vS. salicifolia , L. For the general 
distribution of these species see Text-fig. 1 . 
§ 4. Habit and Habitats of Spiraea Ulmaria. 
S. Ulmaria (= Filipendida Ulmaria , Max.) is a perennial herb with 
a sympodial rhizome which creeps on or just below the surface of the soil 
(Text-fig. 2 ). The aerial parts die back in autumn, leaving the persistent 
1 Densely downy leaves, similar to those of the species mentioned above, are apparently not 
very common in the Rosaceae, though they are met with in various genera, e. g. Rubus , Primus , 
Couepia, &c. 
2 In Rouy et Camus (’00), p. 151, var. 7, S. unicolor , Nob. (= A. denudata , Presl.), is stated to 
be glabrous, except for pubescence on the veins below; while var. 5 , glaberrima, Nob., is entirely 
glabrous. 
3H 
