. A textbook of botany for colleges and universities ... Botany. REPRODUCTION AND DISPERSAL 929 Seeds that pass through the alimentary tracts of large animals, such as cattle, are planted most advantageously in their excrements, where, upon germination, the young seedlings find an excellent sup- ply of food materials. Nuts buried by animals, if they chance to escape being eaten, often are favorably placed for germination; it is to be recalled also that some fruits mature in the ground (as in the peanut and the violet), so that favorable planting is sure to result. Some seeds and fruits have fe
. A textbook of botany for colleges and universities ... Botany. REPRODUCTION AND DISPERSAL 929 Seeds that pass through the alimentary tracts of large animals, such as cattle, are planted most advantageously in their excrements, where, upon germination, the young seedlings find an excellent sup- ply of food materials. Nuts buried by animals, if they chance to escape being eaten, often are favorably placed for germination; it is to be recalled also that some fruits mature in the ground (as in the peanut and the violet), so that favorable planting is sure to result. Some seeds and fruits have features enabling them to remain attached to their posi- tion on the ground, notably in such hooked fruits as those of the cocklebur and the burdock; in the seeds of flax and mustard the outer layer becomes mucilaginous when moistened, facili- tating adherence to the substratum. A remarkable seed-planting mechanism is seen in certain hygroscopic fruits, notably in the porcupine grass {Stipa, fig. 1224). Here the fruit is prolonged below into a sharp spine that is clothed except at the tip with hairs that point upward, while above there is a long awn whose basal portion coils into a close spiral when exposed to desiccation, and uncoils when moistened, the tissues being so constructed that the evaporation and the absorption of water are unequally distributed. If the spine-tipped base sticks into the ground, the repeated twisting and untwisting of the awn serve to bury it deeper and deeper in the soil, the upward-pointing hairs preventing any move- [_. ment in the reverse direction. These fruits Fig 1224. — A mature are such efficient penetrating mechanisrns that fruit of the porcupine grass they work readily through clothes or through (Siipa spartm), showing the envelopes in which they are stored, and pene- seed-bearing portion (d) and ' -^iiriLC • -i the long, spirally twisted awn trate even mto the flesh of grazmg ammals. (o); the basal portion or When the fruits of Stipa lie
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
