On the Structure and Biology of the Genus Hottonia. 
BY 
T. L. PRANKERD, B.Sc. 
With Plates XX and XXI and seven Figures in the Text. 
F the two species comprised in this genus, the American representative, 
Vy Hottonia inflata , has apparently never been studied, though the 
European form, Hottonia palustris , has received some amount of attention, 
from several writers, and a few figures have been published. Since, how- 
ever, there have been various misapprehensions, and interesting points of 
structure have been overlooked, an attempt may be made to give a con- 
nected account of some features in this aberrant genus of the Primulaceae. 
As the stem anatomy varies somewhat in different individuals, and 
very greatly at different parts of the same plant, which may be several feet 
in length, much of the work was done by hand sections, but every point 
in structure has been invariably confirmed by microtome series. Chrom- 
acetic and acetic alcohol were used as fixatives, and the most satisfactory 
stains were found to be safranin, gentian violet, and orange G. for the 
seedlings and growing points, and Dr. Land’s combination of safranin and 
aniline blue for the older parts. 
I. External Morphology and Life-history. 
In its typical development, L e. in water a foot or more in depth, 
H. palustris consists of a long trailing rhizome, terminating at the surface 
of the water in a vertical inflorescence axis bearing numerous flowers 
arranged in whorls (Text-fig. i). The oldest part of the rhizome is 
usually found embedded in the mud, and is often branched, the branches 
forming runners which frequently give off vertical, aerial branches — the so- 
called ‘ land forms \ This affords one method of vegetative propagation, 
since, by the dying off of the older parts of the stem, the young plants 
become entirely separate, and, should the water in the pond rise, may 
become new typically developed individuals. 
These facts do not seem to have been recognized for Hottonia , probably 
because the brittleness of the stem usually causes it to break under the 
water (or the soil) when the plant is pulled at all, which perhaps accounts 
Annals of Botany, Vol. XXV. No. XC VII. January, 1911.] 
