292 DR. M. J. SCHLEIDEN ON PHYTOGENESIS. 



parate fibres, we find the full-grown cells in the commencement 

 still perfectly simple in their AAalls. Thus, for instance, I have ob- 

 served this to be the case in all aerial roots in their outer parch- 

 ment-like layer*. Meyen discovered the spiral fibres in Oncidium 

 altissimum, Acropera Loddigesii, Vanda teretifolia, hort. bot. Be- 

 rol. (rectius Brassavola cordatd), Cyrtopodium speciosissimum, 

 Aerides odorata, Epidendron elongatum, Cattleya Forbesii, Colax 

 Harrisonii and Pothos crassinervia. This is still more evident in 

 the true cortical layer of these aerial roots, where I discovered in 

 Colax, Cyrtopodium, and Acropera the far more beautifully de- 

 veloped and much broader spiral fibres. In quite young aerial 

 roots not a trace of them can be found, and their formation belongs 

 decidedly to a process of lignification. 



We may further be convinced of the subsequent period of the 

 occurrence of spiral fibre in the pericarp of the Casuarincs, the 

 cells of which previous to or shortly after impregnation evince not 

 a trace of spiral formation. Meyen has treated these fibrous cells 

 in the envelopes of many seeds in a somewhat stepfatherly way in 

 his Physioloffie, which is the more to be regretted, as these inter- 

 esting and often highly beautiful formations promise many con- 

 clusions respecting the physiology of the life of the cell, espe- 

 cially if we should take occasion to investigate accurately the 

 individual development of several of them. I may be permitted 

 to make a few observations on this head. 



Their occurrence is more extensive than is generally supposed. 

 They occur in the hairs of the pericarp in some Composites, 

 where they were found by Lessing in Perdicium taraxaci and 

 Senecio flaccidus, and by myself in Trichocline humilis and hete- 

 rophylla. 



They occur in the epidermis in many Labiata, for instance in 

 Ziziphora, Ocymum, in most Salvia, e. g. limbata, hispanica, 

 Spielmanni, &c., and lastly in Horminum pyrenaicum. My uncle 



* Meyen called this, in his Phytotomie, p. 163, an outer cortical layer, which 

 ■was situated on the true epidermis of the aerial roots. In recent times some 

 douhts have been raised as to the correctness of this view. It may however be 

 almost incontrovertibly proved that the cellular layer termed epidermis by 

 Meyen possesses actual stomata, which, from their being covered, usually indeed 

 occur only in a rudimental state, frequently manifest a complicated structure, 

 although deviatir.g only in appearance, as in Aerides odorata, but often likewise 

 occur quite in the ordinary form and distinct, as in Pothos crassinervia. More- 

 over it was not Dutrochet, as it would seem from Meyen's Physiologic, p. 48, 

 but Link who first drew attention to this layer. 



