What is "hypocotyls"

Usage examples of "hypocotyls".

Phalaris, manner of bending--Results of the exclusion of light from their tips--Effects transmitted beneath the surface of the ground--Lateral illumination of the tip determines the direction of the curvature of the base--Cotyledons of Avena, curvature of basal part due to the illumination of upper part--Similar results with the hypocotyls of Brassica and Beta--Radicles of Sinapis apheliotropic, due to the sensitiveness of their tips--Concluding remarks and summary of chapter--Means by which circumnutation has been converted into heliotropism or apheliotropism.

They were also able, as well as the hypocotyls of Brassica, to form straight furrows in damp sand, whilst circumnutating and bending towards a lateral light.

It has already been stated that the cotyledons of Phalaris and Avena, the plumules of Asparagus and the hypocotyls of Brassica, were likewise able to displace the same kind of sand, either whilst simply circumnutating or whilst bending towards a lateral light.

It is a curious fact that the hypocotyls of some plants, which are but little developed and which never raise their cotyledons above the ground, nevertheless inherit a slight tendency to arch themselves, although this movement is not of the least use to them.

In rarely or never becoming perfectly straight, these cotyledons differ remarkably from the ultimate condition of the arched hypocotyls or epicotyls of dicotyledons.

Yet we should remember that the circumnutating sheathlike cotyledons of Phalaris, the hypocotyls of Solanum, and the epicotyls of Asparagus formed round themselves little circular cracks or furrows in a superficial layer of damp argillaceous sand.

After hypocotyls or epicotyls have emerged from the ground, they quickly become perfectly straight.

In concluding this section of the present chapter it may be convenient to summarise, under the form of an illustration, the usual movements of the hypocotyls and epicotyls of seedlings, whilst breaking through the ground and immediately afterwards.

Their hypocotyls were secured to sticks, and glass filaments bearing little triangles of paper were affixed to the cotyledons of both.

Generality of the circumnutating movement--Radicles, their circumnutation of service--Manner in which they penetrate the ground--Manner in which hypocotyls and other organs break through the ground by being arched--Singular manner of germination in Megarrhiza, etc.

Filaments were therefore fixed horizontally to two hypocotyls close beneath the petioles of their cotyledons.

Moreover, in several cases little open circular spaces or cracks in the argillaceous sand which surrounded the arched hypocotyls were visible, and these appeared to have been made by the hypocotyls having bent first to one and then to another side whilst growing upwards.

Nevertheless, this explanation does not apply to the Cucurbita, for when germinating seeds were suspended in damp air in various positions by pins passing through the cotyledons, fixed to the inside of the lids of jars, in which case the hypocotyls were not subjected to any friction or constraint, yet the upper part became spontaneously arched.

The position of the hypocotyls was observed during four successive days, and they continued to bend towards the hilum and lower surface of the seed.

Therefore we can hardly doubt that their short hypocotyls have retained by inheritance a tendency to curve themselves in the same manner as they did at a former period, when this movement was highly important to them for breaking through the ground, though now rendered useless by the cotyledons being hypogean.