166 
only much later did it become obvious that many of the supposed 
Simplex plants were producing a greater elongation of some of 
the lobes than is to be found in pure B. bp. simplex. The ratio 
2.08 : 1 here reported for this family^ was derived by waiting 
until the flower-stems were about 5 — 10 centimeters high, and 
then Galling everything tenuis which produced at least one lobe 
more elongated than those of pure-bred B. bp. simplex. Plate V 
shows the most highly developed leaf-characters attained in each 
of twenty-six individuals taken quite at random from plants in 
this family, which had been finally classified as B. bp. tenuis. 
In normal, well- developed specimens of B. bp. tenuis there is a 
long series of leaves in the middle („climax") region of the 
rosette, in which there is marked elongation of the lobes (see 
plate III), but in family 09275 many of the plants which were 
finally regarded as B. bp. tenuis, had but one or two leaves in 
which recognized tenuis characters appeared. Thus the wide gap 
which ordinarily separates the dominant and recessive types in 
these hybrid families of Bursa, was in this particular family not 
only reduced to zero, but it appears certain that the heterozy- 
gous and recessive categories overlapped to such an extent that 
many individuals which belonged in the former were necessarily 
classified in the latter : hence the defective ratio is to be explained 
by the failure of dominance of the tenuis characters in the heterozy- 
gotes. 
The cause of this failure of dominance is not apparent. The 
environment has a very considerable influence in determining the 
various features of Bursa plants, and especially in limiting the 
development of such distinctive characters as ordinarily appear 
only in the climax leaves. Crowding in the seed-pans, poor 
illumination, and other unfavorable conditions, have caused many 
plants in certain .of my cultures, to develop flowers and ripen 
seeds without having developed their leaves beyond the early 
juvenile stages. While the rosettes in 09275 were not in any 
sense juvenile, the simplex characters do represent a less highly 
special ized type than tenuis , and therefore any influence which 
tends to abbreviate the cycle of development, might conceivably 
reduce tenuis plants to a form indistinguishable from simplex. This 
large family of 656 individuals was germinated in a single square 
seed-pan, 30 X 30 cm, and the young plants grew in this seed-pan 
for seven weeks before they were potted. Perhaps this long 
