PHYTOGENESIS. 243
it has absorbed the cytoblast. _ In all spiral cells, particularly such as exhibit detached fibres, we find the walls of the fully- developed cells to be perfectly simple at the commencement. For instance, I remarked this in the outer parchment-like layer of all aérial roots. [1] Meyen discovered the spiral fibres in Oncidium altissimum, Acropera Loddigesii, Brassavola cordata, Cyrtopodium speciosum, Aërides odorata, Epidendron elongatum, Cattleya Forbesii, Colax Harrisonii, and Pothos crassinervia. This is still more evident in the true cortical layer of those aérial roots, where I discovered in Colax, Cyrtopodium, and Acropera the far more beautifully developed and much broader spiral fibres. There is no trace of them to be found in quite young aërial roots, and their formation pertains decidedly to a process of lignification.
We find further evidence that the spiral fibres do not occur until a subsequent period in the pericarp of the Casuarinæ, the cells of which, previous to or shortly after impregnation, do not evince a trace of spiral formation. Meyen, in his Physiologie, has taken too little notice of these fibre-cells in the envelopes of many seeds, which is the more to be regretted, as these interesting and sometimes extremely pretty formations promise some explanation respecting the physiology of the cell-life, especially if the opportunity should occur of investigating the individual development of several of them accurately. I may be permitted to communicate a few observations on this subject.
Their occurrence is more extensive than is generally supposed. They are found in the hairs of the pericarp in some Compositæ, where they were found by Lessing in Perdicium taraxaci and Senecio flaccidus, and by myself in Trichocline humilis and heterophylla.
- ↑ Meyen, in his Phytotomie, p. 163, called this an outer cortical layer, which was situated on the true epidermis of the aérial roots. Some doubts have recently been raised as to the correctness of this view. It may, however, be almost incontestably proved, since the cellular layer, which Meyen calls epidermis, possesses actual stomata, which, in consequence of their being covered, usually indeed occur only in a rudimental form, frequently exhibit a more complicated structure, although deviating only in appearance, as in Aérides odorata, but often likewise appear of quite the ordinary form, as in Pothos crassinervia. Moreover it was not Dutrochet, as would seem from Meyen’s Physiologie, p. 48, but Link, who first drew attention to this layer.
