MORPHOLOGY OF BLASIA PUSILLA 
44 : 
probably throw light on the question as to whether these plants 
are fertile or sterile. Material kept in the laboratory did not 
prove very satisfactory for this study as conditions were not fa- 
vorable for plant growth. The branches of the thallus had a 
tendency to grow erect and spindling, with much smaller and 
widely separated lobes. 
Advantages of Asexual Reproduction. Cavers 2 says, “It 
seems probable that in both Blasia and Cavicularia we have an 
example of the replacement of spore production by asexual re- 
production. Blasia is found more often with gemma flasks than 
with fruits .’ 7 In the recent observations of Blasia, fruits w T ere 
found quite as abundant as flasks. This problem will make an 
interesting study in connection with seasonal changes and the va- 
riations in environmental factors operating during these seasons. 
Evans 6 has found in species of Metzgeria that gemmae are not 
likely to appear when the plant is growing luxuriantly. 
However, it is the writer ’s theory that vegetative reproduction 
is a safeguard in tiding the plant over unfavorable periods. In 
times of stress for the plant sexual reproduction would be a 
much longer and more uncertain mode of propagation, than that 
of asexual gemmae. Sex organs are formed in the summer but 
spores are not shed until the following spring, while gemmae 
may be fully developed and shed during most months of one 
growing season. 
In the second place it seems likely that gemmae are better pre- 
pared to produce a plant body quickly, than are the spores, be- 
ing so much larger and so abundantly supplied with food. Mac- 
vicar 11 says, “When a plant cannot obtain its normal amount of 
nourishment and especially moisture, it will be smaller and weak- 
er than the type, the stems being shorter and the leaves fre- 
quently deformed. Fruit is not uncommon in this form. The 
other deviation is when the plant has a deficiency of light. Under 
this condition it is generally green or pale green, the stems are 
elongate and thin, the leaves distant and smaller, and if it be a 
thallose species the branches have a tendency to grow erect. In 
such plants fruit rarely occurs but gemmae are often abundant, ’ ’ 
In this case also it would seem that gemma production is more 
abundant under unfavorable conditions. 
