238 
BOTANY: W. J. V. OSTERHOUT 
An answer to this question is suggested by some observations of the 
writer. These were originally made on the cells of the marine alga 
Griffithsia Bornetiana. A cell of this alga is shown in figure 1. Within 
the cell wall {a) is a thin layer of protoplasm {h) which encloses the 
large central vacuole {e). The protoplasmic layer includes numerous 
chromatophores {c). The latter contain chlorophyll and a red pigment 
(phycoerythrin) which is soluble in water. Under normal conditions 
the surface of the chromatophore is impermeable to the red pigment, 
which is thus confined to the chromatophore and prevented from escap- 
ing into the surrounding protoplasm or into the vacuole. 
The writer has observed when one of the larger cells is placed under 
the microscope (without a cover glass) and touched near one end (with 
a needle or a glass rod or a splinter of wood) a change occurs in the 
chromatophores directly beneath the spot which is touched. The sur- 
faces of the chro- 
^ ^ ^ matophores in this 
region become per- 
meable to the red 
pigment, which be- 
gins to difi^use out 
into the surround- 
ing protoplasm. 
This change begins 
soon after the cell 
is touched. As 
the red pigment 
diffuses through the protoplasm it soon reaches neighboring chromato- 
phores and it may then be seen that their surfaces also become permeable 
and their pigment begias to diffuse out. In this way a wave — which 
may be compared to a wave of stimulation — progresses along the cell 
until the opposite end is reached. 
The rate of propagation of this wave corresponds to that of the 
diffusion of the pigment. It would seem that at the point where the 
ceil is touched, pigment, and probably other substances, are set free, 
diffuse out and set up secondary changes as they progress. These 
changes are doubtless chemical in nature. 
The important question then arises, How does the contact initiate the 
outware. diffusion of the pigment or other substances? 
It seems to the writer that this may be due to a mechanical rupture 
of the surface layer of the chromatophore which is either not repaired 
at all or only very slowly. Many cases are now known in which the 
FIG. 1.— A CELL OF GRIFFITHSIA BORNETIANA (IN OPTICAL 
section;, a, CELL WALL; b, PROTOPLASM; c, CHROMATOPHORE 
CONTAINING CHLOROPHYLL AND A RED PIGMENT (PHYCOERY- 
THRIN) WHICH IS SOLUBLE IN WATER; e, VACUOLE FILLED WITH 
CELL SAP. (DIAGRAMMATIC.) 
