194 SUMMARY OK CURRENT RESEARCHES RELATING TO 



Christensen's Index Filicum.* — H. Christ publishes some remarks 

 upon the " Index Filicum " of Carl Christeusen, which has beeh'-in the 

 hands of the public for a little more than a year. The " Index " is a great 

 advance in systematic pteridology, achieving its emancipation from the 

 two cardinal errors of the old Hookerian school, viz. a blind insistence 

 upon the importance of the indusium and sorus as characters for the 

 formation of genera; and secondly, the forcible inclusion of the less 

 well-marked species as varieties and forms under arbitrarily created 

 species-types. Christensen has revived many genera and species created 

 by Presl, Fee and Mettenius, which for years have been treated with 

 suspicion or neglect in the " Species Filicum " and " Synopsis Filicum," 

 Christensen being able to recognise the validity of a genus or species 

 without prejudice to the particular part of the plant in which the 

 proper character is situated. Hence Christensen's system of classification 

 is a natural and not an artificial one. Christ's criticisms embrace ques- 

 tions of geographical distribution, nomenclature, synonymy, the genera 

 of Diel's system, and so on. 



Abnormal Production of Spores in Platycerium.t — H. Poisson 

 describes and figures a plant of Platycerium biforme which in the warm 

 fern-house of the Paris Museum produced spores on the upper surface of 

 one of its sterile fronds. He endeavours to account for this abnormal 

 occurrence. 



Development of Lygodium. J — R. Binford has studied the develop- 

 ment of Lygodium circinnatum with a view to testing its value as an 

 intermediate type in the line of evolution from Marattiacere to Poly- 

 podiacese. Lygodium is chosen as representing Schizaaacege. The author 

 describes his results under the headings : Arrangement and order of 

 sporangia ; the stalk : the tapetum ; the wall ; the sporogenous mass ; 

 sterile sporangia ; relationships. He finds that the family to which 

 Lygodium belongs has some characteristics which cannot be considered 

 as intermediate in the line of evolution mentioned above, but belong to 

 this family only. The sporangium has a marginal initial cell w 7 ith 

 early divisions of the dolabrate (zwei-schneidig) type, and this is not 

 reported for any other ferns. The single sporangium in each sorus, the 

 large sporangium and spores, and the indusium, which in cross-section 

 shows the tissue regions of the foliage leaf, are characteristics which in 

 nature or degree of development belong only to this special group of 

 ferns. Notwithstanding the fact that the Schizagaceaa form a clear link 

 in the chain of evolution of the annulus,-the author considers that the 

 peculiarities mentioned above are so striking and apparently so well 

 established, and the relations of Lygodium are so ancient, that we can 

 hardly consider it to be very close to the evolutionary line that leads to 

 the Polypodiaceae. It seems rather to have appeared very early in the 

 evolution of leptosporangiate ferns and to have progressed in a line 

 somewhat divergent from the main line leading to the Polypodiaceae. 



* Hedwigia, xlvii. (1908) pp. 145-55. 



+ Bull. Soc. Bot. France, liv. (1907) pp. 108-10 (figs.). 



X Bot. Gazette, xliv. (1907) pp. 214-24 (37 figs.). 



