1922] RANDOLPH—MAIZE - 369 
The possibility of the de novo origin of cell organs is one which 
should be more generally recognized. With regard to the plastids 
it must be admitted that the evidence so far obtained by cytologists 
does not permit a definite decision in favor of either the de novo or 
the individuality theory. The exact manner in which plastids 
originate in the cell is obviously of the greatest importance to those 
who are searching for the explanation of the behavior of inherited 
characters which manifest themselves in these organs. If plastids 
are not passed on as permanent individuals, some other explanation 
must be offered for their repeated appearance and regular behavior 
in successive generations. 
Summary 
1. All the chlorophyll types examined were found to contain 
the same initial cell structure, minute ‘“‘proplastids” of the same 
size and general appearance being present in every type. 
2. In normal green plants the proplastid first appears in the cell 
as a minute granule at the limit of visibility, gradually enlarging 
and developing chlorophyll until it becomes a mature chloroplast. 
In plants of the other chlorophyll types studied (Mendelian white, 
Mendelian virescent, and the maternal inheritance strain) the 
unusual characters of the plants are due to the failure of the 
proplastids initially present to develop into plastids with the normal 
size, or color, or both. 
3. The green and colorless plastids found in different plants or 
in different portions of the same plant do not represent two funda- 
mentally distinct types, but are rather to be regarded as the end 
members of a continuous series which comprises also all inter- 
mediate conditions. No cytological evidence was found favoring 
the view that the primordia from which the variously developed 
plastids arise are of more than one kind. 
4. Partially developed and fully matured plastids may be seen 
multiplying by division, but when first visible the proplastid is 
SO minute that it is impossible to determine the mode of its origin. 
The division of partially mature and mature plastids emphasizes 
the fact that they have a distinct individuality at such stages; 
