254 Campbell.— -Contributions to the 
such a view, as the prothallium of the gymnosperms is quite 
as highly developed, and in the cycads, at least, capable of 
independent growth. 
There is, however, an immense interval between the flower 
of the simplest angiosperm and the sporophylls of Isoetes, and 
it would be rash to assume a relationship unless more evidence 
can be produced on the side of the angiosperms to warrant 
this. The possibility of an independent origin of the angio- 
sperms from the pteridophytes has, however, been broached 
more than once, and further investigations with a view to 
settling the matter are very much to be desired. 
