The embryo consists of the folded embryonic leaves in bud (plumule) above, which will grow up on germination as the shoot or “spear,” the short primary root (radicle) below, with in many cases two or more secondary rootlets already showing in its tissues, and from the common “collar” uniting these a more or less prominent shield-shaped organ (scutellum) standing out laterally in contact with the endosperm, the dissolved contents of which it absorbs on germination. (Fig. 38, _s_.) Although typical grasses form a caryopsis as described, exceptions occur. In the exotic _Sporobolus_, _Eleusine_, _Crypsis_ and _Heleochloa_ the fruit becomes truly dehiscent, the seed being loose in the fruit, and the latter opens and allows it to fall out; and in many Bamboos the seed is loose in the _achene_, while in a few cases--e.g. _Melocanna_--the fruit is fleshy and may be as big as a walnut. Returning to the typical grasses. When the fruit ripens in the spikelet, several events may happen. [Illustration: Fig. 40. _Triodia decumbens. a_, “seed,” nat. size; _b_, ditto, × 6. Note the basal hair-tuft and rachilla, and the ciliate, toothed outer palea with a short awn-point, enclosing the inner more delicate palea. Between the two lies the caryopsis. Nobbe.] In most of our grasses the caryopsis comes away trapped between its two paleæ, and the latter bring away with them the small piece of the axis of the spikelet on which they stand: this bit of axis--the _rachilla_--often affords valuable characters in diagnosis. (Fig. 41.) It is the pair of paleæ enclosing their caryopsis which goes by the name of “seed” in most of our grasses. (Fig. 40.) In a few cases, however, e.g. _Panicum_, the spikelet comes away as a whole, so that here the “seed” consists of the glumes, enclosing one, two or more pairs of paleæ with their contained caryopses. Even among our native grasses, however, cases occur where the separation takes place below some of the glumes, and so the “seed,” as met with in samples, consists of glumes as well as enclosed paleæ and caryopsis--e.g. _Anthoxanthum_, _Alopecurus_, &c.--and some care is necessary in examining grass “seed” in these circumstances (see p. 134). [Illustration: Fig. 41. Diagram of a spikelet of a grass--e.g. _Festuca_--comprising six matured flowers and their paleæ, embraced by the two glumes (_g^1g^2_) at the moment of disarticulation as the fruits ripen. The small piece of axis (_a_) left attached to each segment is the rachilla _R_. At _p^2_ the tip of the inner palea is visible protruding from the outer one _p^1_: in the rest it is still enclosed in the latter.]