5I2 THE BOTANICAL EXCHANGE CLUB OF THE BRITISH ISLES. 
may be distinguished from those previously known, and which enable 
the plant to be recognised in the barren state. Another very impor- 
tant contribution is that of Fr. Meister (‘ Memoires de I’Herbier 
Boissier,’ n, 12, 1900). From these, and from verbal statements 
made to me by Dr. Gliick, the following brief descriptions of the 
British forms have been drawn up, hoping that they may induce 
members to study more closely this interesting genus : — 
Clavis. 
A. Submerged floating plants with all shoots of similar form. 
Leaves provided with numerous bladders, and divided into 
numerous hair-shaped terminal segments, the leaf-tips 
toothed on margin. = i. U. vulgaris. 2. U. major. 
B. Shoots differentiated into two forms : (i) green assimilating 
shoots which float in water, and (2'^ colourless shoots which 
are usually subterranean. Leaves divided into 7-20 seg- 
ments. Leaf-tips distinctly flattened. Leaves furnished 
with 0-8 bladders. = 3. U. intermedia. 4. U. ochroleuca. 
5. U. minor. 6. U. Bremii. 
B. 
Bladders chiefly localised on subterranean shoots. The green 
leaves bear no, or only solitary bladders. Leaves with 7-15 
segments. Subterranean leaves with 0-3 bladders. Leaf-tips 
toothed on margin. Winter bud wrapped in a thick whitish 
tomentum. Bud-leaves palmately divided. Segments indented on 
margin and armed with hair-bristles standing together in tufts. = 
3. U. intermedia. 4. U. ochroleuca. 
BB. 
Floating green assimilating, and colourless subterranean shoots 
about equally provided with bladders. Leaves ending in 14-20 
segments and furnished with 0-8 bladders. Leaf-tip smooth on 
margin. Winter buds not covered with a hairy mantle. Bud- 
leaves palmate, with some dichotomous end-segnientS. The 
margin of the bud-leaves is neither indented nor provided with 
tufts of hair. = 5. U. minor. 6. U. Bre^nii. 
