CHAPTERUONMT 
Discussion. 
In the first place we have seen that the organs which 
in some cases envelop the macrosporanges of the Isoetales, 
Lycopodiales and Filicales !) are thin membranous out- 
growths of the sporophyll. Their function is not yet very 
important and probably they serve to strengthen the wall 
of the sporange. À differentiation of the cellular tissue or 
an other characteristic, indicating a more important task 
is still absent. Therefore they are distinctly marked off 
from the testa of the pteridospermous seeds, which im- 
mediately show an other feature. The thin membrane 
investing the sporanges of the Pteridophytes, with no 
trace of composing units, is replaced here by a solid tissue, 
several layers thick, provided with a vascular system and 
exhibiting the indications of a multiple origin in several ways. 
On account of this we may accept that the indusia are 
not homologous with the integuments of the higher developed 
plants and therefore we may exclude them from a further 
comparison. 
Now we come to the pteridospermous seeds and it will 
be my intention to compare them in the first place mutually. 
Afterwards [I will discuss the results obtained from my 
1) From the Filicales I have described no specimens, because the 
features exhibited there are well known, and I could not add any new 
observations. 
