242 PLANT LIFE 
Even among plants nearly related to the 
ferns we find that the prothalli produced by 
the spores tend to differ in their capacity for 
growth. Those which are destined to produce 
eggs are large and well stocked with food, those 
which will produce the sperms are small. 
This difference becomes reflected in the 
spores, and even in the sporangia. 
In the Selaginella plants, often grown in 
greenhouses, certain of the sporangia produce 
a large number of small spores, whilst others 
become much larger, but only bring a very 
few (usually four) large spores to maturity. 
The small spores form a_ rudimentary 
prothallus and a larger or smaller number of 
sperms. It is essential that the number of 
small spores should be kept up, so as to 
maintain a fair chance of a sperm from one of 
them reaching the relatively few available 
female prothalli. 
Passing to the flowering plants, it is difficult 
at first sight to realise that we are only 
witnessing the final stages of an evolutionary 
development of the structures so clearly 
distinguishable in the fern. But so it is, and 
it will be of interest to trace, even briefly, and 
in spite of the wide gaps, the points of resem- 
blance between them. 
The obvious starting-point in both cases is 
the fertilised egg. The fern plant and’ the 
flowering plant each spring from this source. 
The fern closes its life cycle by producing 
spores in the way we haveseen. The flowering 
