6og 
by the Method of Dark-ground Illumination. 
as solid plugs, but as peripheral band-shaped layers of protoplasm lining the 
inside of the wall. There is a clear longitudinal passage through them, as 
sap particles were observed to pass them. 
Plant Hairs, (a) From stem and leaves. 
Cucurbita. 
The large multicellular serial hairs which occur on the stem and leaves 
of Cucurbita spp. proved to be good and interesting objects (Heidenhain, ’ 07 , 
Fig. 251, p. 458, and Fig. 276, p. 487), and useful for the study of 
plasmolysis. 
The hairs employed were taken from growing seedlings. The cell-wall 
of the larger cells is very clearly optically homogeneous, and the cell 
includes only a few inconspicuous chloroplasts. The protoplast consists 
of a layer lining the cell-wall and a number of strands crossing the cell 
lumen, the conformation and direction of these strands constantly changing. 
The general protoplast, with the strings, contains a large number of micro- 
somes, which have rather a vesicular appearance under dark-ground 
illumination. These microsomes, or many of them, are visible with 
transmitted light, but, as in all cases with these minute particles near 
the limits of resolution or visibility, they show much more clearly by dark- 
ground methods ; in fact, they are generally then the most conspicuous 
features of the cell structures. Moreover, with this method of illumination, 
the Brownian movement of the microns in Cucurbita (and other cases) is 
very obvious and can be studied much more readily. 
As in the case of E lode a , the microsomes are carried along by the 
protoplasmic stream, while they also execute Brownian oscillations. It is 
possible to observe also the presence of much smaller particles in the proto- 
plasm. There is what appears to be a slight membrane limiting the pro- 
toplast towards the vacuole, and also forming the surfaces of the strands. 
In no case yet has the nucleus been clearly made out for study. 
The sap particles are as a rule very few, and do not interfere to any 
extent with observations of the protoplast, so that for this, as well as 
other reasons mentioned, these hairs have been useful for the study of 
plasmolysis. 
The streaming in these hairs is, according to Pfeffer, a normal pheno- 
menon (’ 06 , p. 284), but the wounding effect consequent on their removal 
may stimulate them to greater activity in this respect. 
Hairs of Tomato . 
The hairs from the stem of the Tomato are treated in much the same 
way, being removed from the plant and mounted in water. They are serial 
hairs, but only one cell thick (Price, T2). 
