ffiNOTHEKA MUT. LATA AND (E. MUT. SEMILATA. 
551 
in lata x Lainarckiana. The number of latas in this 
cross, as shown by the cultures of de Vries (1913, p. 245), 
fluctuates widely, from 4 per cent, to 45 per cent., though 
most commonly falling near 20 per cent. No doubt the 
environmental conditions at the time when the meiotic 
divisions in the megaspores are taking place, or the physio- 
logical condition of the mother plant at this time, determine 
whether the percentage of latas in the cross will be large or 
small. It is probable that in a similar way environmental 
circumstances control in a measure the wide variations in the 
percentage of the types, such as occur in many CEnothera 
hybrids. 
If functioning megaspores with 7 and 8 chromosomes 
respectively, were formed with equal frequency and had equal 
capacities for development, the cross latax Lama rcki ana 
should yield 50 per cent, of each type. But evidently the 
8-chromosome megaspores have less prospect of functioning, 
since the percentage of latas falls usually to 20 per cent, 
and sometimes to 4 per cent. In certain cases, however, the 
number of latas from a cross rises even above 50 per cent. 
Thus lata x biennis yielded 53 per cent, in 258 plants, and 
lata X biennis cruciata gave 60 per cent, lata (de Vries, 
1913, p. 251). Again, de Vries found that lata x gigas 
gave an offspring about half of which were intermediate 
between lata and gigas, and half intermediate between 
Lainarckiana and gigas. It seems probable that the 
former has 22 and the latter 21 chromosomes. 
The other hereditary peculiarities of lata may be similarly 
explained by the presence of the extra chromosome. Thus, 
Lainarckiana x Hookeri or its reciprocal gives the twin 
hybrids laeta and velutina in I\ (de Vries, 1913, p. 131), 
while lata x Hookeri (1. c., 252), produces,in addition to 
these two types, laeta- lata and vein tin a- lata. There 
can be no doubt that the last two types, which occur in 8-33 
percent, of the offspring, owe their appearance totlie presence 
of the extra chromsome. 
Certain other mutants indicate by their hereditary behaviour 
VOL. 59, PART 4. — NEW SERIES. 36 
