242 HOFMEISTER, ON 



divisions in these directions varies within rather wide 

 limits.* 



The younger portions of the bud of Aspidium jilix-mas 

 are envelopecl in transparent mucilage as is usually the case 

 with all buds.f Owing to the very imperfect exclusion of 

 the outer air from the terminal bud of this fern, in which the 

 punctum vegetationis is only covered by the connivent 

 scales of the older parts, this mucilage is often partly dried 

 up, and forms a structureless membrane, granular on the 

 outside, covering the top of the bud ; precisely similar to 

 that which is seen on the youngest parts of the fronds of 

 Anthoceros.| In order to obtain a clear view of the top of 

 the bud it is necessary to remove this membrane, which is 

 a laborious and uncertain operation. 



The small scales (whose development differs in no essen- 

 tial particulars from that of the similar organs in Nipho- 

 bolus rupestris to which we shall afterwards refer), make 

 their appearance on the terminal bud very far above the 

 point at Avhich the cellular increase of the stem in thickness 

 terminates, but never above the place of origin of the 

 youngest frond (PL XXVI, fig. 14; PL XXXII, fig. 4). 

 This holds good in Aspidium as well as in Pteris, Poly- 

 podium, &c. According to Nageli's definition of leaves 

 and hairs, the scales would undoubtedly belong to the 

 former, as I also formerly assumed to be the case.|| On 

 the other hand a conclusive method of distinguishing 



* This conclusion is the same as that which I arrived at on a former occa- 

 sion from observations on Isoetes (see vol. ii of the 'Abhandl. der K. Sachs. 

 Ges. d. Wiss.' p. 161). The statement there made, that all the septa turned 

 in one of the three directions of the apical cells of the three-furrowed IsoeteEe 

 are at right angles to a plane passing through that indentation of the stem 

 which is nearest to them, is too positive and general. Nevertheless the obser- 

 vations, the number of which was limited by the paucity of the materials, 

 certainly show, that all the septa seen were turned towards one of the indenta- 

 tions ; no one of them was turned towards the space intermediate between two 

 indentations. This fact may have some connexion with the high ratios of the 

 numbers representing the phyllotaxis of those species of Isoetes. 



f See 'Vergl. Unters./ p. 82, note. 



% See 'Vergl. Unters./ PI. i, figs. 8, 9. 



* Zeitschr. f. Wiss. Botanik.,' Heft 3, 4, p. 185. The leaf is formed on the 

 outside at the top of the stem, close under the apical cell, before the growth in 



thickness by peripheral cell-formation is ended The hair, 



&c, is formed on the outside on an epidermal cell by growth of the latter after 

 the termination of the peripheral cell-formation 



|| 'Vergl. Unters.,' p. 87. 



