336 Mottier . — The Development of the Heterotypic 
form of definite and well-defined masses in the same plant, and when such 
occur their number far exceeds the number of chromosomes. When 
all the facts are duly considered, we must admit that there is nothing 
in the resting nucleus that we can look upon as representing a chromosome, 
for all identity of such bodies is lost. In the opinion of the writer, it 
is better not to associate the idea of identity with the chromosomes as 
these are recognized upon the mitotic figure, but this idea should be con- 
nected with smaller units. Whether these units be regarded as hypothetical 
or as objects capable of observation may make little difference in the con- 
struction of a theory, but in order to eliminate as much as possible the 
purely problematic factors, it seems to me best to select as our unit, 
to which we ascribe individuality, some part of the chromatin capable 
of objective demonstration in the resting nucleus. In so doing I have 
selected the term pangen of the de Vriesian terminology chiefly because 
this term has been used in a similar sense by others (Strasburger, ’05). 
Differing somewhat from the meaning put into the term by Strasburger, 
I shall apply the term pangen to the small but distinguishable particles 
that compose the chromomeres. In the spirem, as it emerges from the 
synaptic mass (Fig. 25 a), the chromomeres are seen to be made up of 
smaller granules. These smaller granules, which I shall speak of as pangens, 
can be recognized as well in the resting nucleus. It may be said, of course, 
that each of these granules composing a chromomere can be regarded 
as made of still smaller bodies, and why not apply the term pangen to these 
smaller bodies as others have done ? I have not done so because, if 
we apply the term to objects too small for objective demonstration, it would 
be just as well to apply it to molecule or atom. Furthermore, in using the 
word pangen to designate the small but recognizable granules composing 
the chromomeres, cytologists will have some definite idea of what is meant. 
We shall understand, therefore, that each chromomere is composed of 
a number of pangens, leaving the number indefinite, inasmuch as all 
chromomeres are not the same size, and do not appear to be made up 
of the same number of these granules or particles ; and it may not be 
possible in any case to determine the number of pangens in a given chromo- 
mere. Each chromosome will then be composed of a number of chromo- 
meres, also variable in number. The use of a long series of terms, such as 
pangen, pangenosome, gamosome, and zygosome, as proposed by Stras- 
burger, seems to me to confuse rather than to elucidate, and for the sake of 
simplicity it is better to retain the terminology already established for the 
larger collections of units. Each pangen may be conceived as bearing one 
or more qualities, but how many and what qualities are purely matters 
of theory. 
Turning now to the idea of hereditary qualities or characteristics, the 
following questions present themselves. Do the chromosomes of each 
