objects when examined under the microscope (× about 200). They are spherical, green bodies, each surrounded by two spiral bands attached to the spore at their intersection, s. These bands exhibit hygroscopic movements by means of which the spores become entangled, and are held together. This is of advantage to the plant, as we shall see. All the spores are alike, but some of the prothallia grow to a greater size than the others. The large prothallia produce only archegonia while the smaller ones produce antheridia. Both of these organs are much like those of the ferns, and fertilizationis accomplished in the same way. Since the prothallia are usually diœcious, the special advantage of the spiral bands, holding the spores together so that both kinds of prothallia may be in close proximity, will be easily understood. As in the fern, the fertilized egg-cell develops into an equisetum plant.
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Fig. 299.—Equisetum arvense.
st, sterile shoot; f, fertile shoot showing the spike at a; b, sporophyll, with sporangia; s, spore.
The sterile shoots (st, Fig. 299) appear much later in the season.
They give rise to repeated whorls of angular or furrowed branches.
The leaves are very much reduced scales, situated at the inter-*nodes.
The stems are provided with chlorophyll and act as
assimilating tissue, nourishing the rhizome and the fertile shoots.
Nutriment is also stored in special tubers developed on the rhizome.
