Bower . — Studies in the Phytogeny of the Filicales. 405 
long conducting tracheides of the venation ; and that they project towards 
the lower surface as a continuous band. They are conventionally shaded 
more darkly in the drawing. At the extreme distal apex of the arch shown 
in Fig. 2,0, f, the band of storage tracheides separates from the vein, and 
forms an independent commissure, passing in a lower plane across the course 
of one of the veins. It has even formed an independent process at the apex 
of the curve. This shows clearly how distinct the receptacular xylem may 
be from the conducting veins. 
Comparison suggests that relatively simple-leaved types such as 
B. fraxineum , having few pinnae, originated from a more cojnplex one 
such as B. brasiliense , with many pinnae ; and the latter, very possibly, from 
some doubly pinnate source, a state which actually exists in B. Fraseri and 
volubile , and in Sadleria . But this phyletic aspect does not exhaust the 
interest of the case. The facts may be regarded from the point of view of 
the individual leaf-development. Starting in the ontogeny from the rela- 
tively simple juvenile forms, we may proceed to those leaves which show 
the full normal development of the species. The state shown in B. fraxineum 
might then be held to be an imperfect realization of the more complex 
ancestral form in a type which had passed into a less complex state. The 
archings outwards of this fusion-sorus seen in Fig. 20, e , would thus be the 
expression of a tendency towards separate pinna-formation as in the ancestry, 
but imperfectly carried out in the individual, which had thus advanced 
phyletically in the direction of a simpler leaf. 
It is the relation of these imperfect pinna formations to the veins 
departing from the midrib which stamps their pinna character. We pass 
now to certain developments which stand in strong antithesis to them and 
are not of the nature of pinnae. They arise between the veins. As their 
point of origin is different, so their morphological interpretation must be 
different. They are believed to have led to important modifications of the 
Blechnoid type. The key to these changes is to be found in varieties of 
a well-known species, viz. B. punctulahim , Sw. The normal plant shows 
the ordinary characters of § Lomaria. It is strongly dimorphic, with narrow 
fertile pinnae, but these show occasional signs of interruption of the fusion- 
sori, especially where the condition as regards their breadth is inter- 
mediate between the sterile and fertile. The species is native in South 
Africa and Java. 
Blechnum punctulatum , Sw., var. Krebsii , Kunze. 
The normal plants of the species present no features of importance 
beyond those mentioned. It has been referred by various authors to 
§ Blechnum or to § Lomaria , and is in fact intermediate in character, 
though the fertile leaves are markedly narrower than the sterile. But the 
interest is in the abnormal or varietal forms, which early drew the attention 
