ARRANGEMENT OF CHLOROPLASTS. 271 



where it is suspended in the centre of the cell, it is connected with the 

 pyrenoids by protoplasmic strands. Among Pteridophyta the genus 

 Selaginella affords striking illustrations of the same phenomenon. 

 In the funnel-cells of 8. Martensii (and 8. grandis), each of which, 

 it will be recollected, contains but a single bowl-shaped chloro- 

 plast the nucleus invariably lies at the bottom of the bowl in 

 close contact with the substance of the chromatophore (Fig. IOGa); 

 no less evident is the constant association of the nucleus with 

 the chain of chloroplasts which is commonly found in each of the 

 green parenchymatous cells of the stem (Fig. 6). In the Higher 

 Plants, however, these special relations between nucleus and chloro- 

 plasts (or amyloplasts) are most conspicuous in the case of tissues 

 which are concerned with the manufacture of starch at the expense of 

 other plastic materials. Hence it is particularly in young growing 

 organs and in storage tissues that one finds the chromatophores grouped 

 closely around the nucleus ; they generally disperse when their 

 included starch-grains have grown very large, but may approach the 

 nucleus again, if their starch is once more dissolved {Orchis fusca, Adoxa 

 moschatellina, according to A. Meyer). The nucleus thus appears to 

 exercise a certain amount of control over the formation of starch in 

 chromatophores. This idea is supported by the author's discovery of 

 the fact, that in Selaginella Martensii the included starch-grains are 

 not evenly distributed throughout the bowl-shaped chloroplast, at any 

 rate where the amount of starch is small ; under these conditions they 

 are massed together near the point of contact of the chloroplast with the 

 nucleus, while the rest of the chromatophore is quite free from starch. 

 Further confirmation is provided by Pringsheim's observations which 

 have already been referred to upon the species of Spirogyra which 

 have the nucleus suspended in the centre of the cell ; here, namely, 

 each of the protoplasmic strands that radiate from the nucleus to the 

 chromatophore enters the latter near a pyrenoid. The author has 

 noted something of the same kind in the case of a potato which was 

 turning green through exposure to light ; in this instance, also, most of 

 the protoplasmic strands radiating from the nucleus were connected to 

 the peripheral starch-forming chloroplasts (Fig. 108). 



Attention must next be directed to the influence of external factors 

 upon the arrangement of chloroplasts ; we may begin with the action 

 of light, which was first described by Boehm [in 1856], since which 

 time this phenomenon has been studied by quite a number of 

 investigators. 



An orientating effect of light upon the chromatophores can be 

 readily observed in certain Algae. The axile plate-like chloroplast of 

 Mougeotia does not take up its position in the cell at random ; on the 



