Thomas. — On the P roth allium of Phylloglossum. 407 



ally observed on the peduncle a leaf some distance below the 

 rest of the strobilus, but such a leaf has always been of the 

 sporophyll type. In the Australian form, investigated respec- 

 tively by Bower and Bertrand, to whom we are indebted for 

 most of our knowledge of Phylloglossum, eight was the largest 

 number of protophylls found on a plant, whilst Bertrand 

 urges on anatomical grounds that six is the normal number 

 of protophylls. I have collected plants with twenty proto- 

 phylls, whilst others with ten to fifteen such leaves are of 

 common occurrence. But even in plants richest in proto- 

 phylls no transition occurs between protophylls and sporo- 

 phylls. So far as any evidence here available goes, it would 

 almost seem as if the two structures were not strictly homo- 

 logous. 



To express my meaning in the language of a modern 

 theory, the protophylls may have arisen from the differentia- 

 tion of the lower region of a sporogonium (or the homologue 

 of a sporogonium) in which this region had already acquired 

 sterilised tissues, whilst the sporophylls arose from the upper 

 fertile region of the sporogonium. If so, the protophylls 

 cannot be regarded as sterilised sporophylls. 



There appears to be no necessary connection between 

 the number of protophylls and the reproduction by spores. 

 Plants with two protophylls only may produce a weak spike, 

 whilst plants of twenty protophylls may be barren. 



2. In barren plants the new tuber is formed by the 

 lowering of the apex of the stem, but in fertile plants a new 

 outgrowth is formed, which Bower regards as adventitious. 

 This may doubtless be considered as a form of branching. 

 Neither Bertrand nor Bower observed more than a single 

 tuber formed in the examples at their disposal. Bower, 

 indeed, was inclined to infer that, as no other mode of vege- 

 tative reproduction was known, the plant depended for its 

 multiplication solely upon the germination of the spores. 

 But I have found that the formation of two new tubers is 

 quite a common occurrence, though plants which form a 

 single tuber are still in the majority. The two new tubers 

 may be formed on opposite sides of the plant, in which case a 

 slight dispersion of the plants takes place. Sometimes the 

 two tubers arise close together. Apparently they may be 

 formed almost simultaneously, or in succession. Naturally, 

 it is the stronger plants which most frequently multiply thus, 

 but plants of a smaller number of protophylls may branch in 

 this way. One plant of a single protophyll was found with 

 two tubers forming. 



The occasional occurrence of branching in the strobilus 

 might be interpreted as an indication that the ancestors of 

 the plant were once more abundantly branched. But it 



