No. 449.] STUDIES OA THE PLANT CELL. 



375 



form, which are called chloroplasts when green, chromoplasts 

 when the color is other than green or leucoplasts if colorless. 

 These plastids are without doubt derived from the more primitive 

 chromatophores. 



The colors of chromatophores are various. They are believed 

 always to contain some chlorophyll but this green is frequently so 

 completely masked by other pigments that its presence can only 

 be determined when the additional coloring matters have been 

 extracted. Chloroplasts are universally green excej)t when they 

 may be changing into chromoplasts. Chr()m()i)lasts generally 

 take their tint from the predominance of other stron- i)ii;nK nts 

 in addition to chlorophyll as phycoerythrin in the red ami phyo- 

 phaein in the brown algae. But chromoi^lasts nia\ he (lern etl 

 from chloroplasts whose green has largely or \vliolly (hsa])- 

 peared leaving other pigments present as the yelluw, xanihophyll, 

 or the orange red, carotin. 



The remaining plastids, leucoplasts. are devoid oi color and 

 are found in embryonic regions such as eggs, growmg points, 

 and in the various tissues of seeds, uiulergrouiul oigans anc 

 other structures where the cells are largely or \vholl\ remov ed 

 from sunlight. The leucoplasts may become green ui)on e.\i)o- 

 sure to light thus changing into chloroplasts. 1 hey are respon- 

 sible for the secretion of reserve starch in many structures {c .if. 

 potato) and in consequence have been called amyloplasts. 



Leucoplasts, chloroplasts and chromoplasts are morj^holo-ica y 

 the same structures. It is well known that they nia\ i)ass one 

 into the other in the order indicated and that chloro])lasts^anc 

 chromoplasts may lose their color and become leucoplasts. ^ 

 generally believed that plastids are not formed (/r >/<>:■<>. J he> 

 divide by constriction and thus multii)lying are ])asse(l on lioiii 

 cell to cell and it is beheved froip generation to -eneiation. 

 They are therefore usually ranked as permanent organs of the 

 cell. However, it is but fair to call attention to the lact that 

 there are some serious difficulties in the way ot a conii)cc 

 acceptation of these views. 11' I nts 



The protoplasmic structure of the i)lastids ot n- lei p an s 

 is rather simple while that of the chroniat<<phores m '^j''^^'^ 

 more complex since they contain a special 01 -an Wrmn 



