ETC. 115 



discharge their secretion immediately outwards, as the groups of cells which secrete the 

 nectar of many nectaries, e. g. those at the base of the petals of Fritillaria imperialis, and 

 at the base of the ovary of Nicotiana. The superficial glands are represented frequently 

 and in many different forms by glandular hairs, to which a large number of leaves and 

 stems owe their viscid character, and many leaf-buds their gummy or balsamic coatings. 

 Not unfrequently odoriferous viscid substances collect in the globular terminal cells or 

 knobs of simple glandular hairs ; in other cases the odoriferous oily secretion penetrates 

 through the cell-wall, and raises the cuticle in the form of bladders, collecting beneath it 

 as a clear fluid, while the cells which produce it partially or entirely disappear, as in 

 Salvia, Cannabis, and Humulus (the last on the perianth of the female flowers). We are 

 indebted to a careful work of J. Hanstein's^ for an accurate knowledge of the glandular 

 hairs on the leaf-buds of many trees, shrubs, and herbs. The parts of the bud are coated 

 by a gummy substance, or one composed of gum-mucilage and drops of balsam, which he 

 calls Blastocolla, while the glandular hairs which produce them he terms Golleters. 

 These multicellular shortly stalked hairs springing from an epidermal cell may expand 

 upwards in a strap-shaped manner (Rumex), or may bear cells arranged in a fan on a 

 kind of mid-rib (Cunonia, Coffea), or may form spherical or club-shaped knobs (Ribes 

 sanguineum, Syringa 'vulgaris) ; in Platamis acerifolia branched rows of cells occur, the 

 roundish terminal cells of which become glandular. The colleters attain their full 

 development at a very early period in the bud, when the leaf-structures and portion 

 of the stem out of which they spring are still very young, and consist of tissue which 

 is yet scarcely differentiated. They are borne especially by the enveloping scales of 

 the leaf-buds (Aesculus), by the stipules which precede the leaves in development 

 (Cunonia, Viola, Prunus), the ochreae (Polygonum), or the young leaves themselves 

 (Ribes, Syringa). The secretion of the colleters is a watery mucilage in Polygonum, 

 in the rest it is mixed with drops of balsam (resin). Gum-mucilage always arises 

 from the conversion of a membranous layer lying beneath the cuticle of the col- 

 leter, the substance of which swells on addition of water, and raises the cuticle in 

 places into small bladders (Rumex), or detaches it continuously from the hair as a 

 large bladder; finally the cuticle bursts, and the mucilage escapes and envelopes the 

 buds ; the uninjured inner layer of cell- wall can, on its part, form a cuticle, beneath 

 which a membranous layer again separates, and the process is repeated. Where balsam 

 is also excreted, it may be recognised even in the cells of the hair ; but it appears 

 outside the cell-wall in drops as a deposit in the mucilage, or forms the principal 

 mass of the secretion. Frequently also the young epidermis itself between the colleters 

 participates in these processes (Polygonaceae, Cunonid) ; or these latter are entirely 

 absent, and the blastocolla is produced exclusively from the epidermis ; thus arises, for 

 instance, the greenish balsam on the bud-scales and foliage-leaves of poplars. 



(c) Ihe Sap-conducting Intercellular Passages'-. It has already been explained in 

 Fig. 66 (p. 76), that the 'resin passages' are intercellular spaces, arising usually from 

 the separation of four cells; and they generally acquire a peculiar morphological 

 character from the fact that the cells remain for a considerable time capable of division, 

 and, obeying a common law of growth, form groups the arrangement of which may 

 differ essentially from those by which they are surrounded. The development of the 

 cell-walls is also different, as occurs especially in the resin-passages in the wood of 

 Coniferae. Here the cells which surround the passage are originally like pitted tra- 

 cheides ; but their walls remain thin and unlignified, their cavity enlarges, and their ori- 

 ginal position is obliterated by their growth. The contents of the cells which enclose 

 the passage are more or less like those of the passage itself, since they escape from the 

 one into the other. In Helianthus and other Compositie it is a yellow or red intensely 

 odoriferous oil ; in Umbelliferse a mixture of gum-mucilage and oily or resinous sub- 



' Ueber die Organe der Harz- und Schleimabsonderung in den Laubknospen, Bot. Zeitg. 1868, 

 no. 43 et seq. Compare the veiy instructive illustrations to this paper. 



2 MuUer in Jahrb. fiir wissen. Bot. V. p 387, 1867.— Thomas, ditto, IV. pp. 48-60. 



I 2 



