The seed of the common dandelion, so dear to children in their play-hours, when they amuse themselves by puffing at the white plumy globes which tip the ripe dandelion flower-stalks, is a very interesting object even to their parents, on account of its beautiful structure, and the wonderful way in which it is adapted to the place which it fills. Fig. 45 represents the seed portion of one of these objects, together with a part of the parachute stem, the remainder of that appendage being shown lying across the broken stem. The shape of the seed is not unlike that of the valerian, but it is easily distinguished from that object by the series of sharp spikes which fringe its upper end, and which serve to anchor the seed firmly as soon as it touches the ground. From this end of the seed proceeds a long slender shaft, crowned at its summit by a radiating plume of delicate hairs, each of which is plentifully jagged on its surface, as may be seen in Fig. 46, which shows a small portion of one of these hairs greatly magnified. These jagged points are evidently intended to serve the same purpose as the spikes below, and to arrest the progress of the seed as soon as it has found a convenient spot. Fig. 42 is the seed of the foxglove, and Fig. 43 the seed of the sunspurge, or milkwort. Fig. 47 shows the seed of the yellow snapdragon; remarkable for the membranous wing with which the seed is surrounded, and which is composed of cells with partially spiral markings. When viewed edgewise, it looks something like Saturn with his ring, or, to use a more homely but perhaps a more intelligible simile, like a marble set in the middle of a penny. Fig. 48 is a seed of mullein, covered with net-like markings on its external surface. These are probably to increase the strength of the external coat, and are generally found in the more minute seeds. On Fig. 50 is shown a seed of the burr-reed; a structure which is remarkable for the extraordinary projection of the four outer ribs, and their powerful armature of reverted barbs. Fig. 51 shows another form of parachute seed, found in the willow-herb, where the parachute is not expanded nearly so widely as that of the valerian; neither is it set upon a long slender stem like that of the dandelion, but proceeds at once from the top of the seed, widening towards the extremity, and having a very comet-like appearance. Two more seeds only remain, Fig. 49 being the seed of Robin Hood, and the other, Fig. 52, that of the muskmallow, being given in consequence of the thick coat of hairs with which it is covered. Many seeds can be well examined when mounted in Canada balsam. CHAPTER VI Algæ and their Growth--Desmidiaceæ, where found--Diatoms, their Flinty Deposit--Volvox--Mould, Blight, and Mildew--Mosses and Ferns--Mare’s-Tail and the Spores--Common Sea-weeds and their Growth.