EXTERNAL CHARACTERS 



627 



Osmundaceae and Matonineae, and occasionally in other genera, for instance 

 in Cyathea and in Pteris. On the other hand, axillary branches are found 

 with a high degree of constancy in the Botryopterideae and Hymeno- 

 phyllaceae. In other Ferns buds are found in varying relation to the 

 leaf-bases, and at various other points upon the leaves : all these appear 

 to be different in their nature 

 and origin from the terminal, 

 dichotomous branches above 

 mentioned. 



The architecture of the 

 leaves of Ferns, with their 

 complex and variable out- 

 lines, presents features which 

 are important for comparison. 

 For long the developmental 

 interest centred in the apical 

 segmentation, as exhibited in 

 the Leptosporangiate Ferns 

 with their single initial cell. 

 It was not till 1874 that 

 Sadebeck extended that in- 

 terest to the marginal growth 

 of the ultimate pinnules, and 

 showed in the case of Asplen- 

 ium Shepherdi that the last 

 branchings of the veins are 

 true dichotomies (Fig. 347). 

 The same was shown later by 

 Prantl in the Hymenophyl- 

 laceae : such dichotomy may 

 be held to be wide-spread in Ferns, and its results are apparent in the 

 external outline of many young leaves ; for instance, it cannot be missed 

 in the case of Allosorus crispus, quoted by Goebel (Fig. 348) : here the 

 successive pinnules are produced as branches of a dichotomy, and are 

 successively relegated to a lateral position right and left : the whole pinna 

 is thus a sympodial development of a dichotomous system, though when 

 mature it presents an appearance of pinnation. 



Dichotomous branching is a very obvious feature even in the mature 

 leaves in some of those Ferns which are believed to be relatively primitive. 

 For instance, in the Schizaeaceae, and especially in Schizaea itself, while 

 the same is seen with modifications in the pinnae of Lygodium. 1 Again, 

 in Matonia and Dipteris it is very obvious, though with sympodial develop- 

 ment of the branches; and in the Hymenophyllaceae, especially in the 



1 See Prantl, Unters. z. Morph. d. Gefasskryptogamen. I. Die Hymenophyllaceen 

 Die Schizaeaceen. 



FIG. 348. 



Allosorus crispus. Outline of a leaflet. The branching is 

 clearly dichotomous. The apex has divided into lobes i and 2, 

 of which i is the stronger and continues the growth, 2 forms a 

 lateral lobe. Below we have lobes 3 and 4 which have been 

 similarly formed. The leaf-spindle (rachis) S, is only a narrower 

 portion of the lamina which is subsequently mechanically 

 strengthened. Magnified. (After Goebel. ) 



