368 BOTANICAL GAZETTE (MAY 
division only, it would still remain to be shown whether or not 
the same would hold true for stages before the bodies have 
become large enough to be seen. The writer has repeatedly 
satisfied himself that the series of stages observed actually 
grades off to the lower limit of visibility. 
In view of the uncertainty regarding the mode of plastid origin 
in young meristematic cells, it seems probable that the question 
of the genetic continuity of plastids would not be answered with 
lity by a study of the gametes by methods at our command. 
‘In the present research the gametes have not been observed. 
If it were found that the fertilized egg contains no visible pro- 
plastids, the presumption would be strong in favor of the de novo 
origin of these bodies in embryonic cells. It is conceivable, 
however, that proplastids too minute to be observed might never- 
theless be present and be multiplying only by division. On the 
other hand, if the fertilized eggs were found to contain proplastids, 
the mode of their origin and multiplication would probably be no 
easier to determine than in older meristematic cells which have 
been studied and described. It therefore seems that the impos- 
sibility of determining the mode of proplastid origin in meristematic 
cells requires that the question of the continuity of plastids shall 
remain an open one, regardless of any condition which one might 
expect to observe in the gametes. In view of these facts, explana- 
tion of plastid behavior which are based on the assumption of a 
complete individuality on the part of these organs are unsound. 
The only other alternative is that of de novo origin. The conception 
of the cytoplasm as a substance in which certain processes become 
localized, with the accompanying new differentiation of regions 
which are cell organs, has been furnished with a clear statement 
by HARPER (35), as follows: 
What seems to me the most important advance in our knowledge of cell 
architecture has been in the direction of the recognition of localized spatially 
differentiated regions of the cell body in which certain processes occur . - - 
the plastid is to be regarded as a region of the protoplasmic complex rather 
than a differentiated and definitely delimited body cytologically the 
chloroplast is perhaps little more than an area of the cytoulastn impregnated 
or infiltrated with chlorophyll. 
