PHYTOGENESIS. 243 



it has absorbed the cytoblast. Id 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 laj 

 of all aerial roots. 1 Meyen discovered the spiral fibres in 

 Oncidium altissimum, Acropera Loddigerii, Brassavola cordata, 

 Cyrtopodium speciosum, Aerides odorata, Epidendron elongatum, 

 Cattleya Forbesii, Colax Harrison)}, and Pothos crassinervia. 

 This is still more evident in the true cortical layer of tho 

 aerial roots, where I discovered in Colax y Cyrtopodium t and 

 Acropera the far more beautifully developed and much broader 

 spiral fibres. There is no trace of them to be found in quit 

 young aerial 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 Casuarin 

 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 iibre-cells in 

 the envelopes of many seeds, which is the more to be re- 

 gretted, 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 lew 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 Perdicium 

 taraxaci and Senecio flaccidus, and by myself in Trichocline 

 humilis and heterophylla. 



1 Meyen, in his Pbytotomie, p. 1G3, called this an outer cortical layer, which ^.^ 

 situated on the true epidermis of the aerial roots. Some doubts have recentlj been 

 raised as to the correctness of this view. It may. however, be slmosl incontestably 

 proved, since the cellular layer, which Meyen calls epidermis, possess) I actual 

 mata, which, in consequence of their being covered, usually indeed occur onl) in a 

 rudimental form, frequently exhibit a more compUcated structure, although deviating 

 only in appearance, as hx Ae rides odorata, but often likewise appeal of quite the 

 ordinary form, as in Pothos crassinervia. Moreover it was not Dutrochet, as would 

 seem from Meyen's Physiologie, p. is, hut Link, who firsl drew ittention to this 

 laver. 



