Fig. 33. Beech (Fagus sylvatica).
Fig. 34. Sycamore (Acer pseudo-platanus), showing cotyledons and first and second pair of leaves.
To begin at the beginning, How rarely do we find the embryo of any species represented in a collection of dried plants? It ought to be there, not only as essential to the complete presentment of the history of the species, but as in certain cases indicating relationships which are not apparent when the plant is more advanced. Those who have not observed them would be surprised to find how much variety of form exists in the cotyledons alone, from the fleshy cotyledons of many of the Leguminosæ, the horse-chestnut, &c., to the foliaceous ones, or seed-leaves, of other plants. Among the latter may be noted and compared the lobed or palmate cotyledons of the lime ([Fig. 32]); the glossy dark green, somewhat kidney-shaped ones of the beech ([Fig. 33]); and the pinnatifid ones of the common garden cress (Lepidium sativum); the obcordate ones of the mustard or radish; the long, narrow, thin ones of the sycamore ([Fig. 34]); the sinuous or corrugated and bilobed ones of the walnut, and many more which will occur to the observant reader, or which may be collected by anyone who will take the trouble to watch the germination of plants. And by making such collections, unexpected discoveries may arise, which will yet further confirm what has been said about the variety in form and structure even in these beginnings of growth. Plants which are, on account of their general affinities, reckoned among the dicotyledons, may be found on investigation to have but one cotyledon, as Dr. Dickson observed to be the case with two of our butterworts, Pinguicula vulgaris and P. grandiflora, the third species, P. lusitanica, being dicotyledonous; or even to be acotyledonous, as is the case with the dodder (Cuscuta). In the latter-named genus, it is of importance to collect young specimens, as showing that the plant, although parasitic as soon as it comes in contact with a suitable foster-plant, is of independent origin. A search among young plants will no doubt lead to the discovery of some abnormalities, such as tricotyledonous embryos and other irregularities. Of some plants, such as the furze, the true leaves can only be found at an early stage of growth; in others, much variation may be noted in many points between the first leaves and the more perfect ones which succeed them; some, as the holly, at once developing leaves similar to those which are produced throughout the life of the plant, and others going through many modifications before the ultimate shape is attained, as in the ash, elder, ivy, maple, &c.
The roots or rhizomes also require to be much more fully represented and carefully collected than is usually the case. In every instance where the size of the plant does not prevent, the subterranean and subaqueous parts should be carefully procured and preserved.
Dr. Trimen has lately directed attention to the corm-like tubers of the water plantain (Alisma),[G] closely resembling those of the arrowhead (Sagittaria), which have been described and figured by Nolte, but "do not seem to have been observed, or at least properly understood, in this country. They are buds remaining dormant through the winter, and containing a store of nutriment, to be employed in the development of the new plant from the tuber in the next year." Similar bulbs are developed by the frogbit (Hydrocharis). In determining many grasses and rushes, it is of importance to ascertain whether the rhizome is creeping or cæspitose, and it is therefore essential to collect good specimens. In the case of such plants as the coral-wort (Dentaria bulbifera) and toothwort (Lathræa squamaria), the root-stocks are eminently characteristic. Of such parasites as the broomrapes (Orobanche), some care is requisite in obtaining specimens in which the connection between the parasite and its foster-plant may be preserved and shown. The absence or presence of tubers should also be noted, and if present, they must be represented.
[G] 'Journal of Botany,' 1871, p. 306.