468 Prof. Alexander Dickson on 



With regard to Frullania and Madotlieca {Porella), 

 Leitgeb gives the following explanation of his views : — - 



" In Frullania," lie says, " if the leaf from whose base a branch 

 springs be carefully examined, one is readily convinced that it wants 

 the helmet-shaped lower lobe (the auricle), and sees that the branch 

 arises exactly in the place of this lobe. On its ventral aspect the 

 branch is subtended by a leaf directed obhquely towards the base 

 of the main axis ; and from its position, certainly, this leaf might be 

 viewed as belonging to the main axis, and as representing the lower 

 leaf-lobe, did not its form— corresponding exactly with that of the 

 amphigastria — and the complete absence of any connection with 

 the corresponding upper leaf-lobe make such an assumption seem 

 questionable. The history of its development, moreover, shows that 

 this leaf belongs to the lateral branch, being, in fact, its first leaf, of 

 the amphigastrial series. I have given this example fhst because 

 here the pecuUar helmet-like form of the lower lobes prevents 

 their being confounded with the very differently shaped amphi- 

 gastria. In Madotlieca the relations are not so manifest, since here 

 the lower leaf-lobes pretty closely resemble the amphigastria ; but 

 here, also, a more careful examination shows that the leaflet obliquely 

 subtending, on the ventral aspect, the place of origin of the branch 

 is not a lower leaf-lobe belonging to the main axis, but is the first 

 amphigastrial leaf of the lateral branch.''* 



In support of this view, Leitgeb appeals to the develop- 

 ment of the parts from the segments successively cut off 

 from the apical cell, and states that the lower half of the 

 Initial Leaf-cell, instead of going to form a low^er leaf- 

 lobe, or auricle, assumes the character of an apical cell, and 

 goes on to the development of a lateral branch. 



If these lateral branches originate in substitution for 

 leaf-auricles, as is stated by Leitgeb, it cannot but be 

 regarded as very surprising, and as subversive of our 

 ordinary ideas of the relation of leaf to axis. A philoso- 

 pher, like Mr Herbert Sj)encer,t may propound the mor- 

 phological absurdity of the substitution of flower-buds for 

 the petals and stamens of the flower of an Umbellifer, 

 without its calling for serious comment ; but when a 



* Leitgeb, " Ueber die Yerzweigung der Lebermoose," Bot. ZeiL, 1871, pp. 

 557 et seq, 

 \ Principles of Biology, vol. ii., Appendix A. 



