The size varies from lengths of 2 mm. or less (Poa, Aira) (Figs. [43], [44]) to 15-20 mm. or more (Arrhenatherum) (Fig. [47]) and distinction must be made between the various characters of the caryopsis devoid of its coverings (paleæ, glumes) and such as really belong to the latter.
The caryopsis proper may be short and stout and devoid of a groove—"Millet-seed" type (Fig. [45])—but is oftener elongated, like a grain of Wheat, and then has the characteristic longitudinal groove on the face opposite that where the embryo is situated (Fig. [46]). Details of shape—e.g. cylindroid, fusiform, flattened, &c.—are also of diagnostic value.
In many cases the “seed," consisting of the caryopsis closely compressed between the paleæ, is boat-shaped, e.g. Lolium perenne, Festuca elatior. If this “boat" is long and narrow it may be termed barge-shaped, e.g. Brachypodium sylvaticum, &c. (Figs. [71], [72]): if short, broad, and open or shallow, the term coracle-shaped seems to apply, e.g. Bromus arvensis (Fig. [73]).
| Fig. 44. Aira cæspitosa. The minute “seed" (nat. size) is seen to the right, and the caryopsis (nat. size) to the left of c, the caryopsis, × 8. a and b, the "seed," × 10. The basal awn is about as long as the palea, and the rachilla is very hairy. Nobbe. | Fig. 45. Phleum pratense. Millet-seed type. a, “seed," nat. size; b, ditto, × about 7; d, caryopsis, nat. size; c, ditto, × 7. The rounded caryopsis in b is only loosely covered by one palea. Nobbe. |
Fig. 46. Boat-shaped “seed" of Glyceria fluitans. a, nat. size; b and c, × about 6. d, caryopsis, × about 10. Note the 5-7 strong nerves, and the slender cylindrical rachilla. Cf. Figs. 57 and 58. Nobbe.
| Fig. 47. Arrhenatherum avenaceum. The “double seed” (a and b) consists of two pairs of paleæ with their enclosures. The lower pair (γ) are devoid of fruit, and the outer palea has a long twisted and kneed basal awn: the upper pair (β) enclose the fruit, and the palea has a short straight awn. Note the stiff basal hairs. a, nat. size; b, × about 6; c, caryopsis, nat. size; d, ditto, × 6. Nobbe. | Fig. 48. Lolium temulentum. Type of boat-shaped “seed" with sub-terminal awn arising from between two teeth. c, "seed," nat. size; a and b, ditto, × 6. Note the large smooth rachilla. Nobbe. Cf. Fig. [57]. |
Further important distinctive characters are obtained from the absence or presence of awns, and the peculiarities—length,
