396 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
the chromosomal substance, as in certain species of Ascaris, or, as in some 
insects, by the inclusion in certain cells of particular cytoplasmic substances. 
If, and so far as, these occurrences effect a differential distribution of cel¬ 
lular potentialities, rather than something like a stimulus to a particular 
cellular development, they constitute deviations, from the condition of 
primary totipotence which is probably as truly the general rule for the 
cells of animals as it is for the cells of plants. 
The potentialities whose manifestation marks each particular type of 
cell in a vascular plant come to expression—under ordinary conditions— 
in a definite order. This orderly development seems to be determined in 
part by an inherited tendency to pass through a definite sequence of phases— 
a tendency which now applies to all the alternative life histories upon one 
of which the cell has embarked. But the orderly development is also 
partly dependent upon a progressively changing environment, which con¬ 
sists largely of other cells among which the one in question is firmly held. 
The importance of the environment is shown by the fact that, although 
the course of development of any cell of a massive plant seems to be less 
easily diverted to an alternative course than is that of a protist or of a cell of a 
coenobe, the cellular life history is, nevertheless, not rigidly fixed. In some 
cases, and for a limited time at least, it is subject to reversal—dedifferentia¬ 
tion. It is capable for a considerable time of being greatly modified by the 
onset of changed conditions. The stimulus that causes the formation of a gall 
may determine the expression of potentialities that otherwise would not 
be manifested either in the organ affected or in any other part of the plant. 
Thus the whole range of cellular potentialities may not be exhibited in a 
plant living under what we call “ normal ” conditions. To comprehend 
the extent of this range it is necessary to observe the plant under all condi¬ 
tions, including pathogenic, that it is capable of enduring. 
In the course of the development of an embryonic cell into a differ¬ 
entiated tissue element, the structural peculiarities that usually characterize 
embryonic cells are modified. But the cell may still remain essentially 
embryonic. Next, perhaps, it becomes itself incapable of taking on char¬ 
acters other than those proper to the cells of the tissue of which it has be¬ 
come a part; but, so long as it retains the power of dividing, it can still 
transmit to its offspring its full initial complement of potentialities. Finally 
it may, and in many cases probably does, while still alive and otherwise 
functional, lose all power of division, and therewith its embryonic character. 
The story that is presented, therefore, in ontogenetic development is 
that of a plant, simple or complex, composed of totipotent cells all begin¬ 
ning life with the power of transmitting their totipotence to their offspring. 
However complex the plant, many cells retain this power, remaining em¬ 
bryonic until they divide or become moribund. Others, undergoing marked 
changes in structure and in function, may in time lose their totipotence 
and their power of division. But so long as they can divide, they can give 
