Note * — Chapter XV · DROSOPHYLLUM—RORIDULA—BYBLIS—GLANDULAR HAIRS OF OTHER PLANTS—CONCLUDING REMARKS ON THE DROSERACEÆ.

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 moderately 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 foot-stalks (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 (excluding the flower-stems) must have borne the astonishing number of 2,568,099 glandular hairs. The hairs were counted late in the autumn, and by the following spring (May) the leaves of some other plants of the same lot were found to be from one-third to one-fourth broader and longer than they were before; so that no doubt the glandular hairs had increased in number, and probably now much exceeded three millions. [page 356]