97 



Plastids. 



D. M. MOTTIER, Indiana University. 



(Abstract) 



The major part of the results of an extended study on plastids and 

 similar bodies in cells of various plants, of which the following is an 

 abstract, has been published in the Annals of Botany, Vol. .32, pp. 91-114, 

 1918. 



The investigation was concerned chiefly with the origin of leuco- 

 plasts and chloroplasts from their primordia, as found in meristematic 

 cells. The primordia of leucoplasts and chloroplasts appear as very 

 minute, granular or rod-shaped bodies, which multiply by direct division. 

 From such priinordia, leucoplasts develop as rounded or pear-shaped 

 bodies with the starch inclusion accumulating within. In case the pri- 

 mordium is rod-shaped, the leucoplasts, in such tissues as the root tip of 

 Pisum, take on the foi'm of a hand mirror with the inclusion in the larger 

 end. 



In certain typical cases the primordium of the chloroplast may first 

 become lenticular with a pale center and a densely-staining periphery. 

 With further growth they finally assume the form present in the adult 

 plant organ. 



Morphologically the primordia of leucoplasts and chloroplasts are 

 precisely alike. It may be of interest to note that the morphological iden- 

 tity of leucoplasts and chloroplasts was pointed out by A. F. W. Schimper 

 about thirty-eight years ago. The following is a translation of his sum- 

 mary (Bot. Zeit., p. 899, 1880) : "The results of this brief study show 

 that the deep chasm hitherto supposed to exist between the starch form- 

 ers in assimilating and in non-assimilating cells does not, in fact, exist. 

 In cells free from chlorophyll there are definite organs which generate 

 starch, and these organs are none other than undeveloped chloroplasts 

 (Chlorophyllkorner), which under the influence of light are able to de- 

 velop into the latter. On the other hand, chlorophyll grains are not 

 always organs of assimilation merely, but they may, in the conducting 

 tissues and in cells which contain reserve material, function as starch 



7—11994 



