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." Meyen discovered the spiral fibres in 
Oncidium altissimum, Acropera Loddigesii, Brassavola cordata, 
Cyrtopodium speciosum, Aérides 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 aérial 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 Casuarina, 
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 re- 
eretted, 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 obser- 
vations on this subject. 
Their occurrence is more extensive than is generally sup- 
posed. They are found in the hairs of the pericarp in some 
Composite, where they were found by Lessing in Perdiciwm 
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 sto- 
mata, 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. 
