536 
li. RUGGLES GATES AND NESTA THOMAS. 
15 chromosomes. These individuals belonged to eight 
distinct cultures from various diverse sources^ numbering iii 
all 504 plants. They, moreover, were all derived, immediately 
or more remotely, from races having 14 chromosomes. 
Certain cytological features of these 21 individuals may 
now be considered, beginning with the somatic divisions. 
In cult. 228, although seventeen buds of plant No. lY . 17 
(semi lata) were microtomed, no reduction divisions were 
found; but over thirty counts of somatic mitoses showed the 
number of chromosomes to be constantly fifteen. Figs. 1-7 
(PI. 35) are drawn from somatic divisions in this individual, 
showing two prophase and five metaphase stages. In some 
cases the chromosomes are evidently in pairs and the odd or 
extra chromosome^can be identified without much difficulty 
(figs. 5-7), but in the majority of cases the pairing is not so 
marked (figs. 3, 4). There is, therefore, no constancy in the 
degree of pairing in the various metaphase figures of an 
individual, though the odd chromosome is often easily dis- 
tinguished. 
There is considerable variation also in the size, shape and 
thickness of the chromosomes, though their number is 
constant. Fig. 5 shows a case where one chromosome is 
considerably smaller than the remaining fourteen, a fairN 
common variation in the lata plants, shown also in biennis 
lata (fig. 8). Occasionally, as in fig. 7, one chromosome has 
a median constriction giving it a dumb-bell appearance, and 
not infrequently a constriction appears near one end of a 
chromosome, as in fig. 9,^more or less completely pinching off 
a small portion. 
In the lata plant No. 228. lY . 20 over tAventy exact 
somatic counts were made, the number of chromosomes beiug 
15 in each case. Fig. 10 shoAvs a clear pairiug of certain 
chromosomes iu a nucleus of this individual ; and in fig. 11 
one of the chromosomes is exceptionally small, and the pairs 
are A^ery Avell marked. 
Ill making chromosome counts the utmost care Avas 
exercised, and only nuclei Avere selected in Avhich the number 
