Cuar. XVI.] SECRETION, ABSORPTION, DIGESTION. 311 
some way down the leaf; but the glands soon began to dry, viz. after 
35 hrs. The leaves of Erica tetralix began to act in 7 hrs. 30 m., but 
never caused much secretion; nor did the bits of leaf of the saxifrage, 
though in this case the glands continued to secrete for seven days. 
Some leaves of Pinguicula were sent me from North Wales, to which 
leaves of Erica tetralix and of an unknown plant adhered; and the 
glands in contact with them had their contents plainly aggregated, as 
if they had been in contact with insects; whilst the other glands on 
the same leaves contained only clear homogeneous fluid. 
(15) Seeds.—A considerable number of seeds or fruits selected by 
hazard, some fresh and some a year old, some soaked for a short time 
in water and some not soaked, were tried. ‘The ten following kinds, 
namely, cabbage, radish, Anemone nemorosa, Rumex acetosa, Carex 
sylvatica, mustard, turnip, cress, Ranunculus acris, and Avena pubescens, 
all excited much secretion, which was in several cases tested and found 
always acid. The five first-named seeds excited the glands more than 
the others. The secretion was seldom copious until about 24 hrs. had 
elapsed, no doubt owing to the coats of the seeds not being easily 
permeable. Nevertheless, cabbage seeds excited some secretion in 4 hrs. 
30 m.; and this increased so much in 18 hrs. as to run down the leaves. 
The seeds, or properly the fruits, of Carex are much oftener found 
adhering to leaves in a state of nature than those of any other genus ; 
and the fruits of Carex sylvatica excited so much secretion that in 
15 hrs. it ran into the incurved edges; but the glands ceased to secrete 
after 40 hrs. On the other hand, the glands on which the seeds of the 
Rumex and Avena rested continued to secrete for nine days. 
The nine following kinds of seeds excited only a slight amount of 
secretion, namely, celery, parsnip, caraway, Linum grandiflorum, Cassia, 
Trifolium pannonicum, Plantago, onion, and Bromus. Most of these 
seeds did not excite any secretion until 48 hrs. had elapsed, and in the 
case of the Trifolium only one seed acted, and this not until the third 
day. Although the seeds of the Plantago excited very little secretion, 
the glands continued to secrete for six days. Lastly, the five following 
kinds excited no secretion, though left on the leaves for two or three 
days, namely, lettuce, Erica tetralix, Atriplex hortensis, Phalaris 
canariensis, and wheat.. Nevertheless, when the seeds of the lettuce, 
wheat, and Atriplex were split open and applied to leaves, secretion was 
excited in considerable quantity in 10 hrs., and I believe that some 
was excited in six hours. In the case of the Atriplex the secretion ran 
down to the margin, and after 24 hrs. I speak of it in my notes “as 
immense in quantity, and acid.” The split seeds also of the Trifolium 
and celery acted powerfully and quickly, though the whole seeds 
caused, as we have scen, very little secretion, and only after a long 
interval of time. A slice of the common pea, which however was not 
tried whole, caused secretion in 2 hrs, From these facts we may 
conclude that the great difference in the degree and rate at which 
various kinds of seeds excite secretion, is chiefly or wholly due to the 
different permeability of their coats. 
