No. 449.] STUDIES ON THE PLANT CELL. 379 



•described by Palla ('94) in the chromatophores of several of the 

 Conjugales and have been named caryoids. Caryoids (Fig. 2, 

 ^r i) are smaller and more numerous than pyrenoids and are 

 distributed irregularly in the chromatophore but chiefly along 

 the edge. Their function is not known. 



The leucoplasts complete the list of plastid structures. They 

 are colorless and may be found in underground or other portions 

 of the plant removed from light or where there is little or no 

 photosynthetic activities as in embryo sacs, seeds, growing points, 

 etc. They become impregnated with chlorophyll under condi- 

 tions suitable for photosynthesis thus chahging into chloro- 

 plasts. An important function of the leucoplast is the forma- 

 tion of reserve starch in various parts of the plant. The more 

 recent investigations of this process (Meyer, '95, Salter, '98) 

 claim that it is in the nature of a secretion within the substance 

 of the leucoplast. This view is opposed to the older conceptions 

 {Schimper, '81, Eberdt, '91), which regarded the starch grain as 

 formed by the direct change of proteid material in the plastid. 

 In view of Timberlake's ( : 01) studies on the pyrenoid of Hydro- 

 dictyon we may well hesitate to fully accept the views of Meyer 

 and Salter and ask for further investigations of this very difificult 

 subject. In addition to starch leucoplasts may contain proteid 

 crystals and oil globules. 



The reproduction of plastids and their evolutionary history 

 in ontogeny and phylogeny offers a very attractive field for 

 research. It is well known that plastids multiply by fission and 

 it is generally believed that they never arise de novo but are 

 passed from generation to generation as permanent organs of 

 the cell. The process of division may be very favorably studied 

 in the spore mother-cell of Anthoceros (Fig. 2, t 4). The fission 

 begins (Davis, '99) by a constriction at the surface as though 

 the bounding membrane of cytoplasm exerted pressure upon an 

 ■elongating structure. There is no evidence that the interior of 

 the chloroplast undergoes any changes that could assist the 

 process further than a possible tendency of the two separating 

 portions to gather their substance together as division proceeds. 

 The conditions suggest that the division is a mechanical separa- 

 tion of material too bulky for the best advantages of the cell. 



