574 ; REPORT—1905. 
exttuded into the water. But it may be seen also in the chloroplasts of the higher 
plants when these are large enough to be examined easily. In these cases the 
green colouring matter appears granular when the chloroplast is in the epistrophe 
or shade position, fibrillar when it is in the apostrophe or intense light position. 
This difference in the appearance of the chlorophyll accompanies a difference in 
the shape of the chloroplast. As is well known, the chloroplast in the epistrophe 
position presents an oval or more or less circular form; in the apostrophe 
position a flattened and lenticular form. The fibrillar structure appears to 
be that of fine fibrils lying more or less parallel, but a closer examination shows 
that they are connected together here and there so as to give the impression 
of an elongate network. In the epistrophe condition the chlorophyll corpuscle 
appears greener than in the apostrophe condition, The granules are in fact 
so arranged and so numerous as to present a practically continuous surface 
of chlorophyll to the action of the light rays. The fibrillar arrangement, on the 
contrary, has numerous light spaces between the fibrils, so that less surface of 
chlorophyll is exposed to the rays of light. The difference in the amount of chloro- 
phyll surface exposed to the light appears therefore to be bound up with the differ- 
ence in the intensity of light which causes the different positions of epistrophe and 
apostrophe to be assumed by the chloroplast. Just as in diffuse light the chloro- 
plasts themselves are more fully exposed to the light than in intense light, 
so in the individual chloroplast we appear to have such an arrangement of 
the chlorophyll that in diffuse light a larger surface of it is exposed to the 
light rays than in a more intense light. The interesting conclusion is there- 
fore arrived at, that the chloroplast is able, not only by its position but also by its 
structure, to guard itself against the effects of a too intense light. 
‘A careful examination of the chloroplast in the epistrophe position renders it 
probable that the granular appearance is not due to the existence of separate 
granules of chlorophyll. It resembles more nearly an optical effect, due to the 
superposition of alveoli upon one another, such as appears in fine oil-foams. By 
focussing carefully above and below the granules we get a distinct appearance as 
of a green alveolar network. If the chlorophyll corpuscle is extruded into water 
it begins to swell up and becomes vacuolar; the granules disappear and the 
chlorophyll then appears to be distinctly diffused through the ground substance of 
the chloroplast. Jam therefore inclined to the view that the chlorophly] corpuscle 
consists of a ground substance in the form of a delicate alveolate structure, in 
which the chlorophyll is more or less uniformly diffused. The diameter of the 
threads of this network is greater in the epistrophe than in the apostrophe 
position, and this affords a means by which the chloroplast can accommodate itself 
to varying intensities of light. 
The chloroplast must be regarded as performing at least two functions. It 
3 about the dissociation of CO, and it is a starch-forming organ. In the 
algae and some other plants these two functions appear to be differentiated, and 
starch is formed directly by the pyrenoid. How far these two functions are 
independent in the ordinary chloroplast is not known; but that starch can be 
formed, independently of chlorophyll, in the leucoplasts and in the ordinary 
chloroplasts directly from sugar and other organic solutions in the dark seems to 
indicate that the two are not necessarily connected. 
The colourless stroma of the chloroplast gives a distinct and pronounced re- 
action for phosphorus when treated according to Macallum’s method. It resembles, 
therefore, in this respect the nuclein constituent of the nucleus. What the exact 
significance of the presence of phosphorus in the chloroplast may be I do not know, 
but it is extremely interesting to find that in an organ in which a high degree of 
metabolic activity is always found a substance should be present which is akin to 
the highly organised nuclear constituents. It suggests an interesting comparison 
with those plants in which a special starch-forming organ, the pyrenoid, is dif- 
ferentiated. For the pyrenoid, as Macallum has shown, and J am able to confirm, 
gives a strong reaction for phosphorus, whilst the chromatophore with which it 
is associated gives but a slight reaction for this element. This seems to indicate 
that the starch-forming function is bound up with the presence of phosphorus 
bring 
