266 PHOTOSYNTHETIC SYSTEM. 



chloroplasts are distributed among a number of small corpuscles. This 

 type of chlorophyll apparatus possesses the following additional advan- 

 tages : first, enhanced mobility of the whole apparatus, a factor which 

 reacts favourably upon photosynthetic activity in a way which will be 

 explained in more detail below ; secondly, acceleration of the efflux 

 of synthetic products ; and, lastly, a more even distribution of light 

 throughout the chlorophyll apparatus, especially when illumination is 

 feeble. 



In many cases chloroplasts have the power of changing their shape 

 in response to external influences, particularly photic stimulation. 

 Micheli, Moore, Senn and others have shown that, among Algae and 

 Mosses, and also in Phanerogamic palisade-cells, the chloroplasts con- 

 tract and become rounded or hemispherical in very intense sunlight 

 (as well as after prolonged darkening). 



As regards the internal structure of chloroplasts, it has come to 

 be generally accepted, in consequence of the researches of Pringsheim, 

 A. Meyer and Schimper, that the chlorophyll-corpuscle of the Higher 

 Plants consists of a colourless spongy protoplasmic matrix or stroma, in 

 which are embedded a number of green viscous drops or granules, the 

 grana. Such a granular structure is very evident, for example, in 

 the case of the chloroplasts of Orchids and Fern-prothallia ; in Algal 

 chromatophores, on the other hand, the grana are exceedingly minute 

 or quite unrecognisable, and the same statement applies to Antlioceros. 

 In certain cases treatment with water reveals a peculiar system of 

 curved radial striae ; this striation was observed first in Bryopsis by 

 Posanoff, and subsequently in Antlioceros by Schimper, while the author 

 has found it to be particularly conspicuous in Sdaginella Martensii. 

 The striated appearance only becomes evident after swelling has taken 

 place ; what the corresponding internal structure may be, is a matter 

 for further enquiry. 



It is not yet definitely known in spite of the researches of 

 Von Mohl, Nageli and others whether chloroplasts are invested 

 by special membranes or not. Most botanists, it is true, agree 

 with Von Mohl that, in general, no visible plasmatic membrane 

 is present. There are, however, undoubtedly some exceptions to 

 this rule ; in Sdaginella Martensii, for example, the bowl-shaped 

 chloroplast found in each photosynthetic cell (Fig. 106 a) possesses, 

 on its concave side, a somewhat highly refractive, relatively thick 

 (about '3-*4 n in thickness) and granular plasmatic membrane, which 

 may possibly represent a special light-perceiving apparatus. 



The characteristic pigments of chloroplasts 138 are soluble in alcohol. 

 Crude alcoholic " chlorophyll-extract " contains both green and yellow 

 colouring matters, which may be separated from one another by shaking 



