36 REVUE BRYOLOGIQUE 
The whole of the following remarks applies to the Yorkshire 
Plain — a large tract of flat land very little above the sea-level. 
LE HyYPNuM ADUNCUM 
At Naburn, 4 miles from York is a small marshy piece of ground 
close by the railway line. Sometimes there is sufficient water to 
make a pool which supports chiefly Z'ypha latifolia. The pool dries 
up each year, except for a little water here and there, and at this 
time there is abundance of Hyp. aduncum var. polycarpon at the 
foot of Typha and rushes. The var. intermedium grows in one 
part and I have little doubt that it gives rise to the var. poly- 
_Carpon, With its crowd of slender branches. 
Along one side of this marsh grows Æyp. Sendineri forma 
vulgaris, and it is safe to say that this originates from the 
abundant Hyp. aduncum close by. This Sendineri is the true 
typical plant with very short leaves and very strong nerve, and 
it is not difficult to see the relationship between these leaves and 
those of the var. polycarpon. The green colour is common (o +4 
both. 
On Sirensall Common is a very small pool so hidden by tall 
grasses that it is invisible from the road close by. On 31 Déc. 
1896 T found here Hypn. aduncum var. paternum forma gracilis, 
distinct at the shallow side of the pool by the pale green slightly 
hooked apices of the stems,which reached nearly to the surface of 
the water. 
In a much deeper pool on Askham Bog, about 40 miles distant, L 
Saw on 25 Apr.1902 a little forest of yellow spikes of Ayp.aduncum 
Var. Palernum ending some distance below the surface of the 
Water. The long branchless apex of the stem in this case was 
evidently due to the growth being too rapid to make branches, 
and the rapid growth was due to the attraction of the illuminated 
surface above. 
On two ponds I have found Hyp. aduncum, Group pseudo- 
fluitans, floaling on the surface of thé water. In these cases there 
were many branches, and the apex was short, the branching being 
evidently due to equal illumination on the whole plant. Both these 
plants approach the var. flexile. To return to the Strensall pool, on 
18 Aug. 1906 I found it dried up the first time after a great many 
visits Lo it, and the place previously occupied by 4. aduncum var. 
pale"rum forma gracilis was now occupied by Æ. aduncum var: 
intermedium, growing in crowded masses round the foot of Scirpus 
lacustris. AÀs the drying up of the pool is of rare occurrence, it 
Would seem that the var. intermedium originated from the var 
