30 Gardiner and I to. — On Mucilage-cells 
and the most important difference between them consists in 
the kind and manner of secretion. The physiological function 
of these glandular structures has already been sufficiently 
treated by Goebeler. One would here briefly point out that 
the mucilage and resin serve a most important purpose in the 
plant-economy, particularly by preventing too excessive trans- 
piration in the young and delicate buds, and by serving as a - 
reservoir for water against times of drought. Similarly the 
woolly hairs protect the plant both from injury from without 
and from the dangerous effects of extreme variations of 
temperature. 
In the present paper we attempt to give a more detailed 
account than has hitherto appeared of the minute histology 
of two forms of mucilage-secreting hairs, viz. those of 
Blechnum occidentals, L., and Osmnnda regalis , L., and we 
also endeavour to describe the various phenomena which are 
associated with mucilaginous secretion. This work was sug- 
gested partly by Prof, de Bary’s remarks upon the mucilage- 
hairs of Osmnnda regalis , L. 1 , and partly by an observation 
made by the first-mentioned of the present authors, that in 
Blechnum brasiliense , Desv., there were mucilaginous hairs 
associated with the young bud. 
II. Method of Research. 
The observation of the secretory structures of which we 
write presents but little difficulty. All but the very youngest 
leaves having been removed from the fern-shoot under exami- 
nation, the developing paleae or the developing leaves are 
separated as required, and then further dissected and teased 
out under a low power of the dissecting microscope. By 
this means hairs of all ages may easily be obtained. 
Fresh material gives by far the most satisfactory results. 
Alcohol causes abnormal shrinking of the mucilage attended 
by great distortion of structure. Saturated watery picric acid 
on the other hand produces great swelling of the mucilaginous 
contents, which finally ends in the rupture of the cell and the 
1 De Bary, loc. cit., p. 99. 
