286 GLANDULAR HAIRS. [Cuar, XV. 
The glands on the flower-stalks and leaves of Primula 
sinensis quickly absorb a solution of the carbonate of ammonia, 
and the protoplasm which they contain becomes aggregated. 
The process was seen in some cases to travel from the glands. 
into the upper cells of the pedicels. Exposure for 10 m. to 
the vapour of this salt likewise induced aggregation. When 
leaves were left from 6 hrs. to 7 hrs. in a strong solution, 
or were long exposed to the vapour, the little masses of 
protoplasm became disintegrated, brown, and granular, and 
were apparently killed. An infusion of raw meat produced 
no effect on the glands. 
The limpid contents of the glands of Pelargonium zonale 
became cloudy and granular in from 3 m. to 5 m. when they 
were immersed in a weak solution of the carbonate of am- 
monia; and in the course of 1 hr. granules appeared in the 
upper cells of the pedicels. As the aggregated masses 
slowly changed their forms, and as they suffered disintegra- 
tion when left for a considerable time in a strong solntion, 
there can be little doubt that they consisted of protoplasm. 
It is doubtful whether an infusion of raw meat produced any 
effect. 
The glandular hairs of ordinary plants have generally 
been considered by physiologists to serve only as secreting 
or excreting organs, but we now know that they have the 
power, at least in some cases, of absorbing buth a solution 
and the vapour of ammonia. As rain-water contains a small 
percentage of ammonia, and the atmosphere a minute quantity 
of the carbonate, this power can hardly fail to be beneficial. 
Nor can the benefit be quite so insignificant as it might at 
first be thought, for a moderately fine plant of Primula sinensis 
bears the astonishing number of above two millions and a 
half of glandular hairs,* all of which are able to absorb 
* My son Francis counted the 
hairs on a space measured by means 
of a micrometer, and found that 
there were 35,336 on a square inch 
of the upper surface of a leaf, and 
30,035 on the lower surface; that is, 
in about the proportion of 100 on the 
upper to 85 on the lower surface. 
On a square inch of both surfaces 
there were 65,371 hairs. A moder- 
ately fine plant bearing twelve leaves 
(the larger ones being a little more 
than 2 inches in diameter) was now 
selected, and the area of all the 
leaves, together with their footstalks 
(the flower-stems not being included): 
was found by a planimeter to be 
39°285 square inches; so that the 
area of both surfaces was 78°57 
square inches. Thus the plant (ex- 
cluding the flower-stems) must have 
borne the astonishing number of 
