356 Bower —A Theory of the 
stages are over. The advantages of direct nutrition, and of 
perennation of the vegetative system are, from the point of 
view of spore-production, obvious enough, and a greatly 
increased output of spores became thereby possible. 
The second point, viz. the substitution of discrete arche- 
sporia for one concrete one would also be a great biological 
advantage : as the size of the single sporogenous mass in- 
creases, the difficulty of supply of food to all the developing 
spores makes itself increasingly felt, while further the risk of 
mechanical damage becomes more serious : for during the 
semi-fluid condition of the contents of the sporangium, where 
all the sporogenous cells are separate from one another, a large 
sporangium is mechanically ill-protected, while a single punc- 
ture by animal or other agency would ruin the whole. Again, 
separate loculi may be matured in succession, thus not making 
a simultaneous demand for nutrition, while keeping up a supply 
of spores for an extended period. From the point of view of 
nutrition and protection, therefore, septation would appear to 
be a biological advantage. 
Thirdly, from the point of view of dispersal, a projection of 
the sporangia beyond the general surface is clearly a gain : 
the mechanical difficulties of scattering the spores from pro- 
jecting sporangia being much less than from deeply seated 
ones. Thus on various grounds we should be prepared to 
expect septation and separation of sporangia to appear in 
increasing degree in an ascending evolutionary series. 
We shall next inquire if among living Vascular Cryptogams 
there is any evidence which would support the idea that 
septation has taken place : and the answer is to be found in 
the frequent occurrence among them of synangia, such as 
those of Tmesipteris , P silo turn , Danaea , Marattia , Kaulfussia , 
Ophioglossum . Moreover, the sporangia, when distinct from 
one another, are so grouped in many Pteridophyta as to 
suggest a common origin from a synangial body by separation 
and rounding off of the individual sporangia : this is the case 
with the sori of many Leptosporangiate Ferns. The develop- 
ment of the sporangiophore of Equisetum suggests a similar 
