392 
Gates and Rees. — A Cytological Study of 
the point of union in metaphase is at the ends of the chromosomes, and 
the phenomenon appears to differ from that in Lactuca only in its greater 
precision and in its uniformity for the individual. 
In the Jamaican Locustidae a similar situation has been described 
(Woolsey, 1915). In the genus Jamaicana the basal number of chromo- 
somes in the males is thirty-five, but some of the chromosomes unite during 
meiosis in certain species and individuals. The chromosomes form a graded 
series, the X being the largest. In the spermatogonial metaphase two 
chromosomes of unequal length unite to form a V while their mates remain 
separate. This was the condition in seven of the ten individuals belonging 
to the three species studied. In the three exceptional individuals, one 
from each species, the conditions were as follows : (i) Two pairs of • 
associated rods forming unequal V ’s. This gave the appearance of thirty- 
one chromosomes. These Vs separate after the spermatogonial divisions. 
(2) One large V was formed, each arm being composed of a pair of 
chromosomes united end to end. (3) The two unequal Vs were formed, 
but in the first maturation division they united to form an elongated ring, 
the Vs separating on the heterotypic spindle. In this genus a multiple is 
usually accompanied by the X-chromosome. They appear to be attracted, 
but are not brought into union as in Hesperotettix , Mermiria , and 
Chorthippus. 
The possible relations of these unions of lettuce chromosomes to 
genetic phenomena as a basis for partial coupling and modification of the 
Mendelian ratios has been discussed elsewhere (Gates, 1920, p. 221), and 
need not be considered again at this time. 
f 
Chromosome Numbers in Lactuca. 
The chromosome counts of Ishikawa (1916) disclose considerable 
variation in this genus, the x number ranging from five to twenty-four. 
There are five pairs of small chromosomes in L. denticulata , L. Keiskeana , 
L . lanceolata and its var. platyphylla. In L . lanceolata the chromosomes 
apparently differ conspicuously in size. In L. stolonifera Ishikawa finds 
eight pairs of extremely small chromosomes, and in L. Tamagawensis eight, 
often seven, very small bodies. As all the counts were made during the 
meiotic divisions, the occurrence of seven bodies in some cases points to 
a fusion of chromosomes similar to that here described in lettuce. In 
L. villosa and L. laciniata there are nine pairs of chromosomes, and they 
are much larger, apparently agreeing with those of lettuce in their main 
features, though L. laciniata has larger chromosomes than L. villosa. In 
L. Thunbergiana the chromosomes are similar in size to those of the last 
two species, but there are twelve pairs of meiotic chromosomes, or frequently 
eleven, probably as a result of temporary coalescence of two pairs during 
meiosis. L. debilis is yx as regards chromosome numbers, having twenty- 
