EPIDERMIS. 



99 



dies off'. Hanstein has termed these organs which cover the buds with a sticky secretion 

 ' Beleimer,' or Colleters, and their sticky product bud-ghie, or Blastp-colla. 



There is as yet only one case known to me in which such mucilage, covering buds, 

 has an origin other than that indicated. The bases of the young leaves of Osmunda- are 

 covered with a rich amorphous mucilage. This originates from long septate hairs, with 

 large bead-like cells, each of which, in the stages of development observed, is completely 

 filled with a mass of mucilage. The origin of the latter remains to be investigated. On 

 treating with water, the mucilage swells and escapes as an amorphous hyaline mass from 

 the burst cellulose membrane. 



Sect. 20. The capitate hairs with mealy dust — pili pulveriilend — should at pre- 

 sent, for the sake of consistency, be separated from the glandular hairs, but they must 

 be treated in immediate relation to them. To these hairs the under-surfaces of the 

 leaves of the so-called gold and silver ferns owe their dusty covering, which is white 

 (Gymnogramme tartarea, calomelanos and other species, Notholaena nivea, Cheilanthes 

 spec.) or golden yellow (Gymnogramme sulfurea, Martensii, &c., Pteris aurata), while 

 on the foliage of the mealy Primulas it appears light yellow (Pr. marginata) or usually 

 white (Pr. Auricula, farinosa, &c.). 



The mealy covering of these plants is not excreted Hke the wax coverings, by 

 the whole epidermis, but exclusively by the globular apical cells of small hairs, which 

 are borne on a short unicellular (Gymnogramme) or two-celled (Primula) stalk (Fig. 

 43) *. It appears on the whole surface of the apical cell in the form of rods or small 

 needle-shaped crystals. In Gymnogramme 

 these radiate from the whole surface of the 

 apical cell ; their length may greatly ex- 

 ceed the diameter of the latter. In the 

 Primulas they are irregularly aggregated. 

 In not quite intact specimens, especially 

 of the Primulas, they are often shattered 

 to heaps of small fragments, and scattered 

 over the whole epidermis. The covering 

 consists of resinous bodies '', which are to 

 a great extent easily soluble in cold alcohol. 

 In Gymnogramme I found, after solution 

 in alcohol, a finely granular residue, which 

 dissolved in ether. Klotzsch ^ names the 

 bodies in question Pseudo-stearoptene : they are, according to his statement, 

 which certainly requires revision, easily crystallised out from the alcoholic solution 

 (I obtained only aggregates of very small crystals) : the crystals are rather hard, 

 heavier than water, fusible at 50°, sublimated without change when air is excluded, 

 slightly aromatic, soluble in warm water (?!), alcohol, ether, acetic acid, and alkalies. 



On the foliage of many plants closely allied to those in question — Filices, Primula 

 sinensis, &c. — instead of the dusty hairs, there are found typical resin-secreting, 



Fig. 43.— Gymnogramme tartarea. A (142) dusty liair from 

 the under surface of the leaf, floating on water; the round 

 apical ceil covered by the erect radiating rods cf resin. — B 

 (375) a similar hair after momentary action of cold alcohol ; 

 the rods are for the most part dissolved ; in their place remains 

 a finely granular layer, which is quickly dissolved in ether. In 

 the apical and stalk-cells are nuclei ; the larger granules in the 

 apical cell are chlorophyll grains. 



* See Reinke, /. c. 



° S. Milde, Monogr. Generis Osmiindae, Vindob. 1868. 



^ Link, Icones Selectoe, Heft IV. Tab. III. figs. 7-9. — Mettenius, Filices horti Lipsiensis, p. 42. 

 ■• Goppert, N. Acta Acad. Leopold. Carol. XVIII. Suppl. I. p. 206. 

 ^ Monatsber. d. Berlin. .Acad. 1851, Dec. Botan. Zeitg. 1852, p. 200. 



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