403 
Physiology of Ptilpy Fruits. 
spaces are found to be covered with a substance of mucila- 
ginous or gelatinous nature, and which is obviously related to 
the cell-wall itself. The substance is very transparent and 
homogeneous, and may readily escape observation altogether 
unless staining reagents are employed, and these have to be 
used with some care, because if water be applied to the sections 
previous to staining, it rapidly swells up and disappears. 
Haematoxylin, Bismarck brown, and Hanstein’s violet all gave 
fair results, but the two former reagents were by far the most 
satisfactory. If the section of material which has been pre- 
served in alcohol be rapidly washed with water, and then 
stained with Kleinenberg’s haematoxylin, the mucilage appears 
as a glairy substance lying in the intercellular spaces and 
around the edges of the section ; but if the sections are stained 
at once without rinsing with water the mucilage is seen in its 
unswollen condition. In this state (e.g. after staining) it 
refuses to swell up, owing perhaps to the alum in the reagent, 
and the same is true of chromic acid material. 
It is found either lining the cell-wall or aggregated in little 
drops, and in the latter state the drops most frequently occur 
at places where two cell-walls meet. As the fruit grows 
older the mucilage becomes more and more apparent, and 
when sections of alcohol material which is almost ripe are 
placed in water, a very rapid separation of the cell-layers is 
seen to take place, due to the expansion and swelling of the 
intercellular mucilage. It is best studied in alcohol material, 
since if fresh fruits are cut the protoplasm also issues from the cut 
cells and interferes with the observations, as it is itself of a glairy 
consistence, and is so abundant as to mask everything else in 
sections of younger fruits. It appeared possible that the entire 
mucilage might be derived from this source, but the contracted 
primordial utricles, which are present in alcohol material, 
showed no trace of the substance in their interior, nor was it 
present in the space left between them and their cell-walls. 
Still, the extremely sharp line of demarcation which exists 
between the non-swollen part of the cell-wall and its mucila^ 
ginous investment gives at first some support to the idea that 
