Phytogeographical Excursion in the British Isles. 11 7 
with regal’d to the British form, but I should prefer the expla¬ 
nation that we have, on the Continent, two forms, N. alba and 
N. Candida, and besides these, in the western part of Europe, our 
plant, which may also occur in Norway (in our Copenhagen 
herbarium 1 have seen a poor specimen which may be referred to 
it). This form seems to inhabit pools and small lakes in moors, 
while the true N. alba (as we saw it in the Norfolk Broads), 
prefers less “acid-humus” water. The true N. Candida is a 
northern and eastern form; R. Caspary, “ Botan. Notiser,” 1879, 
says “ per Europam et Asiam borealem et arcticum et in regione 
montana Germanise, Austrise et Asia (Himalaya); our form is the 
western substitute ; the main species N. alba occurs in the whole 
of Europe and Siberia (excluding the Arctic part), and also in 
Algeria. 
I recommend the form here described to closer examination 
and comparison with the other forms, preferably under cultivation. 
It is smaller in all directions than the ordinary N. alba; 
Leaves 9-12 cm. broad, 11-13 long ; diameter of the flower 8-9 cm. 
Cistace^:. 
Helianthemum nummnlarium (L.) Dunal (— H. chamce- 
cistus Mill), v. tomentosum (S. F. Gray). 
W. Grosser (Cistacese, in Das Pflanrenreich, 1903), has 
divided this species into two sub-species, and C. K. Schneider 
(Handb. d. Laubholzkunde, 8. Lief., 1909) follows him in this 
regard ; while E. Janchen (Die Cistaceen Osterreich-Ungarns, in 
Mitteil d. Naturv. Vereins an der Universitat Wien, 1909) has 
several separate species under the species collectiva H. chamcecistus 
Mill. 
Whether we follow the first or the latest author, we find 
two “ forms ” occurring in the more northern (not alpine) parts of 
the area of the species collectiva. The question then arises which 
form occurs in the British Isles, or do both forms occur? 
As far as I have seen, only the var. tomentosum (S. F. Gray) is 
British (while in Denmark we have almost only the other form : 
var. hirsutum, Thuill.), but I have had very few specimens from 
Great Britain at my disposal, and further examination of more 
ample material may result in discovering the other form also. 
The var. tomentosum is easily distinguished by the felty, whitish 
underside of the leaves ; var. hirsutum has the underside of the 
leaves green and covered with sparse steleate hairs. 
As the two forms do not differ from each other in other more 
important respects, I find it more natural to follow Grosser and 
Schneider in taking them as two varieties of one species, than to 
consider them as two species as Janchen does. 
Caryophyllace^e. 
Sagina procumbens L. X saginoides (L.) Dalla Torre. = S. media 
Briigg (Syn. S. glabra Druce, 1911, non Fenzl, 1833. 
On Ben Lawers we met in plenty a Sagina with white petals 
about as long as the sepals. As there were many specimens and the 
numerous flowers were open in the sunshine of the forenoon, the 
plant attracted much attention, and caused much controversy 
