406 SUMMARY OF CURRENT RESEARCHES RELATING TO 



As a rule they are permeated by green, brown, or red pigments, with 

 which oily substances are possibly mixed. The chromatophores of 

 certain groups of algaa are characterized by containing a colourless 

 strongly refractive substance, which exhibits a striking resemblance 

 to the chromatin-bodies of the cell-nucleus in its reactions, and espe- 

 cially in its behaviour towards pigments. These bodies, which are 

 of by no means universal occurrence among algfe, and which have 

 elsewhere been observed only in Anthoceros, are termed by the author 

 Pyrenoids. 



Pyrenoids occur in brown, red, and green algfe ; they have usually 

 a spherical form, and are imbedded, either singly or in rows, in the 

 substance of the chromatophore. In the green algfe they are com- 

 monly surrounded by starch, and then constitute the starch-generators. 

 They result from the formation of starch-grains in the substance of 

 the chromatophore, in close proximity to the pyrenoid ; they are at 

 first distinct, but finally coalesce into a hollow sphere. True starch- 

 generators are wanting in the red and brown algte and in Euglena. 



Pyrenoids are capable of growth and of division ; they result from 

 the division of other jiyrenoids, rarely from rejuvenescence. They 

 divide by constriction. When enveloped by a layer of starch, com- 

 j)ound pyrenoids sometimes arise from division, without the envelope 

 dividing at the same time. 



The chromatophores vary in form, size, and colour according to 

 their age. In young cells they are often smaller, paler, and of 

 simpler structure than in the mature parts of plants ; in other cases 

 they lose their colour, as in many hairs and rhizoids, and in secondary 

 meristem. In the antheridia of Characefe they are at first colourless, 

 afterwards red. They have only a limited power of growth before 

 dividing. They divide either by constriction or bisection ; but there 

 is no sharp distinction between the two modes ; or occasionally by 

 multisection. The division of the pyrenoid or starch- generator pre- 

 cedes that of the chromatophore. 



The chromatophores always increase in number by division, never 

 by rejuvenescence from the cell-protoplasm ; as can easily be proved 

 in the simpler forms ; with greater difficulty in the case of multi- 

 cellular algae. The chromatophores of apical cells and of meristem 

 are the direct result of the division of similar structures occurring in 

 the reproductive cells. In certain cases, as in male sexual cells and 

 in many hairs, they are resorbed. Where both sexual cells contain 

 chromatophores, they may either coalesce or remain distinct after 

 conjugation. 



The author regards the chromatophores as an essential constituent 

 of the cell in algte, never absent excei^t when the cell is destined to 

 a special biological function, for which their possession would be 

 unnecessary. 



As regards inclosures in the chromatophores, true starch-grains 

 occur only in the green algse, and there in most species. As a rule 

 it is only green — ^but in the central cells of CharaceaB colourless — 

 chromatophores that have the power of forming starch-grains. They 

 are either distributed uniformly through the entire mass of the 



