SMITH: THE HISTOLOGY OF CERTAIN ORCHIDS 4 
since he considers that the epidermal slime of seeds and endo- 
sperm slime has been shown to originate from the secondary 
thickening of the cell wall. He recognizes four types of epi- 
dermal slimes, as follows: 
1. The inner wall thickened by a secondary slime membrane 
(Althea rosea, Quercus pedunculata, Malva vulgaris, Cornus mas). 
2. The inner wall thickened by a secondary slime membrane 
and upon this a tertiary cellulose lamella (several species of 
Cassia, Ulmus glutinosa, Corylus Avellana, Arbutus unedo are 
a few examples). This type is the most common of the four. 
3. The inner and outer walls thickened by a secondary 
slime membrane and upon this a tertiary cellulose lamella, the 
side walls also thickened (Salix alba the only example of this 
type known to Walliczek). : 
4. The lower cell wall thickened by a secondary slime 
membrane and a tertiary cellulose membrane, a quaternary 
slime membrane, a fifth cellulose membrane and so forth up to 
ten layers which was the largest number observed (Barosma 
vulgaris, B. crenulata, B. serratifolia, B. crenata, and B. betulina). 
In all cases the slime membranes give the reactions of what 
Walliczek calls true slime from their first occurrence. These re- 
actions are swelling in water, precipitation by alcohol, and not 
staining blue with iodine and sulphuric acid. Cellulose slimes 
are described by him as staining blue or violet with these rea- 
gents. Only the mucilage of the seed epidermis of crucifers, of 
Cydonia and of Salvia have been proved to be of this sort. 
Walliczek in considering the slime membranes in the inner 
tissue of vegetative organs notes that with certain treatments 
plant slimes which are to be regarded as arising in the form of 
secondary thickenings show stratification, and that this strati- 
fication is the best morphological distinction between cell 
membrane slime and cell content slime. The latter appears 
quite homogeneous (‘‘Orchis-Schleim”’,“‘Raphiden-Schleim”). He 
notes, however, that proof of the origin of cell content slime is 
certain only in Symphytum and Orchis. There may be also cell 
membrane slimes which do not show stratification. Walliczek 
cites the slime of Tilia grandiflora as an illustration, though it 
is generally classed as a cell membrane slime. In the later 
stages at least he notes also that all slimes may be more or less 
dissolved and that in the stages of solution the stratification 
disappears. 
