Pteridophyten. — Floristik, Geographie, Systematik etc. 217 



and of the root nature of the rhizophore of Selaginella are summa- 

 rized. The following reasons for regarding the rhizophore as a root 

 are given: 1) the absence of foliar organs (this is, however, incon- 

 clusive as the rhizomes of the Psüotaceae, shoots of Trichomanes 

 membranacea and inflorescences of the Cviiciferae have lost the 

 power of forming leaves over part or the whole of their length); 

 2) the downward growth and the absorption of water in a reverse 

 direction to that of growth; 3) the stelar structure which, however, 

 is of little value in determining morphological differences (for example 

 the reduced rhizome of Trichomanes muscoides is very like the rhi- 

 zophore of Selaginella). On the other hand the exogenous origin of 

 the rhizophore supports its cauline nature (though exogenous roots 

 are known); so do the place of origin and the absence of a root cap. 

 Cases have already been recorded in which rhizophores of Selagi- 

 nella develope spontaneously into leafy shoots; the author has 

 observed at Kew structures intermediate in appearance between 

 rhizophores and shoots and in one case at least he observed a fairly 

 complete series of forms from a typical rhizophore to a shoot which 

 resembled a rhizophore chiefly in that it, at first, grew downwards. 

 In a garden hybrid of Selaginella normal rhizophores were produced 

 in the lower moist part of the plant and ordinary leafy shoots 

 higher up; these when kept artificially moist, developed as rhizo- 

 phores. These points and the fact that Velenovsky has described 

 certain Selaginellas showing tetrachotomy, in which the two small 

 shoots occupy the exact position of rhizophores, lead the author to 

 accept the view that the rhizophore is cauline. It is held highly 

 probable that the rhizophore is the homologue of the protocorm of 

 Lycopodimn and quite likely that the organs known as Stigmariae 

 are homologous both with rhizophore and protocorm. 



The protocorm is not regarded as primitive but as a highly 

 modified shoot; as, however, Lang states Lycopodiutn cevnuuni with 

 large prothallus and well developed protocorm is primitive, the author 

 concludes that in the saprophytic species of Lycopoditim this struc- 

 ture has been reduced to vanishing point. Isabel Browne. 



Bergep, A., Stapelien und Kleinien einschliesslich eini- 

 ger anderer verwandter Sukkulenten. III. Handbuch 

 sukk. Pflanzen. (Stuttgart, E. Ulmer. 16«. 433 pp. Mit 79 Abb. 

 1910.) 



Im vorliegenden Bande behandelt der Verf. in vorzüglicher 

 Weise die Asclepiadeen. Eine grössere Zahl neuer Arten beschreibt 

 er. Hat der Verf. doch in seinen Züchtereien herrliches Material, 

 Hanbury unterstützte ihn mit seinen schönen Pflanzen aus dem 

 Garten zu La Mortola. Den praktischen Bedürfnissen des Züchters 

 wird auch vollauf entsprochen. Matouschek (Wien). 



Cowles, C. H., The fundamental causes of Succession 

 among Plant Associa tions. (Rep. brit. Ass. Sc. Winnipeg, 

 Sect. k. p 668—670. 1909.) 



The author's position is best stated by some extracts from his 

 Condensed summary. The time has passed when a mere description 

 of the various plant associations is sufticient, and some attempt must 

 be made to deal with the genetic relationships existing amongst the 

 plant associations. Just as evolution has knit together into a genetic 



