NOTE 40 (page [88])
Precautions in Testing Seed-buoyancy

Many seeds and fruits require a few hours’ soaking before they sink; and when small they will rest a long time on the surface of still water, but a touch with the finger or a drop of water will send them to the bottom. A few will float a few days (3 or 4) before sinking; but such are included in the non-buoyant group. Only in rare cases does prolonged drying increase the period of flotation by more than a few days, examples being given at the end of the Table of Buoyancy results under [Note 10]. Adherent air-bubbles, a common cause of adventitious buoyancy, must always be removed.

NOTE 41 (page [91])
The Buoyancy of the Seeds of Convolvulus Soldanella in Fresh Water and Sea-water compared

The experiments were commenced at the close of September, 1894, and covered six months. At the end of this period in Mr. Millett’s experiment, 56 per cent. of the seeds were afloat in fresh water, and 62 per cent. in sea-water; whilst in my own experiment 72 per cent. floated in fresh water, and 65 per cent. in sea-water. I was indebted to Mr. Millett’s courtesy for the seeds.

NOTE 42 (page [96])
On Secular Changes in Sea-density

Exact data bearing on this subject are not at my disposal; but it would seem that geologists have formed conflicting conclusions from similar premises. There is the view that the composition of the ocean water was very different in early geological periods (Encycl. Brit., x., 221); but I should imagine that the character of the crustacean fauna of those seas would negative any great divergence from the present condition. Suess implies that the ancient seas carried the same minerals in solution that they do now, and it is to be inferred in a similar proportion (E. de Margerie’s French edition of Das Antlitz der Erde, ii., 343 and 345).

NOTE 43 (page [102])
On the Mucosity of Small Seeds and Seed-like Fruits when wet

I paid considerable attention to this subject from the standpoint of dispersal some years ago, and published most of the results in Science Gossip for Sept., 1894. This peculiar quality of seeds had been noticed by Dr. Kerner in his Pflanzenleben (vol. i., 1887-91), and was regarded as illustrating a mode of dispersal of seeds by adherence. As a rule, such seeds when placed in water become coated with mucus in a few minutes, or within an hour, and when allowed to dry on feathers they adhere as firmly as if gummed. I found that this quality is not affected by prolonged drying, as in the cases of Nepeta glechoma and Salvia verbenaca, where it was exhibited to the same degree after the seed-like fruits had been kept from one to three years. I especially tested about 110 British plants that were likely to display this quality, and found that about a dozen exhibited it in a marked degree, and if to these we add those plants with seeds that display it to a limited extent so that they merely become adhesive when wetted, the total would be nearly twenty. It will be noticed from the list subjoined that the plants showing marked mucosity belong to twenty genera and to ten families, the Labiatæ and Cruciferæ predominating. Although in some genera, like Plantago, there is reason to suppose that the seeds of all the species would behave in this fashion, it would be wrong to infer that this is usually the case, six genera being indicated below to which such a rule would not apply, and doubtless the number could be extended. These plants in England mostly occur at the roadside, on waste ground, and in dry meadows. It may be added that although in most cases the seeds appear in water to emit mucus, “exuded mucilage” being the expression used in the English edition of Kerner’s work, in some instances, as with Helianthemum vulgare, there appears to be a dissolving process affecting the outer seed-covering.

I. Plants with Seeds or Seed-like Fruits that emit Mucus to a Marked Degree when placed in Water.