ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 367 



CRYPTOGAMS. 



Pteridophyta. 



(By A. Gepp, M.A., F.L.S.)| 



Phylogeny of the Pteridophyta.* — I. Browne publishes her seventh 

 article upon the phytogeny and inter-relationships of the Pteridophyta, 

 and considers the inter-relationships of the phyla in considerable detail, 

 summarising the conflicting views of various writers upon the subject, 

 for instance, Tansley, Campbell, Lang, Bower, Jeffrey, Lignier, Scott. 



Alternation of Generations based on Ontogeny. — W. H. Lang 

 expounds a theory of alternation of generations in archegoniate plants 

 based upon the ontogeny. The development of an organism from the 

 germ-cell is regarded as due (a) to the properties of the germ-cell, and 

 .(#) to the conditions under which the germ-cell develops. Each stage 

 •of development influences the succeeding stage. Each specific germ- 

 cell develops under normal conditions into its corresponding specific 

 form of the plant. In certain algae (Dictyota, Polysiphonici) there is an 

 alternation of generations distinguished only by the number of chromo- 

 somes in the nuclei and by the reproductive organs ; and the two 

 generations are strictly homologous. In the Bryophyta and Pteri- 

 dophyta there is also a regular alternation of generations very dissimilar 

 in their form and structure, apart from the nature of the reproductive 

 organs and the number of chromosomes. The explanation of the great 

 difference between the two generations is to be sought, not in the 

 cytological differences between the two sorts of germ-cells, but to the 

 very different conditions under which they develop. It is assumed that 

 the haploid and diploid germ-cells have potentially the same morpho- 

 genetic properties and under the same conditions would give rise to 

 similar bodies. The spore, however, develops free, in direct relation to 

 the soil, water, light, etc. The fertilised egg, on the other hand, 

 develops under the protection of the maternal plant-tissues, under their 

 nutritive and stimulating influences. In the Bryophyta the maternal 

 influence and protection last throughout the development of the sporo- 

 gonium. In the Pteridophyta the young sporophyte after a while 

 becomes free from the prothallus ; but the lines of development 

 initiated under the influence of the parent-prothallus determine the 

 further course of development. In the flowering plants the case is 

 reversed, and it is the gametophyte which develops within the body of 

 the sporophyte. In these cases of parental association it is to be noted 

 that the nursed organism produces an effect upon the tissues inclosing 

 it ; for instance, the calyptra that grows up around the young sporo- 

 gonium in Aneura or Antfioceros, and perhaps the coats of the ovule and 

 seed. As regards the phylogenetic problem of the origin of the two 

 generations in the Archegoniate, the origin is to be sought in some 

 ancestral algae with a haploid or sexual and a diploid or asexual 

 generation of similar form and of alternating recurrence. The 



* New Phytolog., viii. (1909) pp. 51-72. t Tom. cit., pp. 1-12. 



