44 SCIENCE PROGRESS 



ing types : (a) Stolons, in which the plagiotropic shoots are 

 overground, with long internodes, and bear foliage leaves ; 

 (b) Suboles, where likewise the internodes are elongated, but 

 the leaves are reduced to scales and the structure as a whole 

 is pale-coloured. A modification of this type is presented in 

 those cases where the terminal region is enlarged as a food 

 reservoir ; (c) Rhizomes, a term restricted to thick plagiotropic 

 shoots with short internodes from which the aerial shoots 

 arise ; (d) Rhizodes, which resemble suboles except that the 

 lateral shoots develop from definite main buds, as in Hippuris 

 and Eleochoris ; (e) Creepers and leaf-bearing suboles, in which 

 the plagiotropic shoots, whether overground or underground, 

 do not arise from the base of an erect shoot ; (/) Rootstocks 

 in which the underground stem is erect. Numerous examples 

 of all these types are described, together with a consideration 

 of their biological features. The length of the internodes 

 appears to be largely dependent upon the density of the sur- 

 rounding soil, whilst the direction of growth, though mainly 

 related to gravity, is in some cases even more dependent upon 

 moisture (e.g. Tussilago). The level of growth is related to a 

 variety of environmental factors, such as the physical con- 

 dition of the soil, its aeration, moisture, temperature, chemical 

 reaction, amount of nutrients and biotic relations. 



The underground shoot, which is regarded as a modification 

 of the aerial, is particularly prevalent in certain types of 

 habitat. Thus in Denmark, of the species exhibiting this 

 modification, 34*5 per cent, occur in woods and hedgerows, 

 30-09 per cent, on wet soil and the remainder in a variety of 

 habitats. 



The present writer has investigated the floral structure of 

 Eranthis hyemalis, Ficaria verna, Anemone nemorosa, Aconitum, 

 spp., and other Ranunculaceae {Ann. Bot. Journ.). In most of 

 these the " curve " of meristic variation for the andrcecium and 

 gynseceum is multi-modal in character, the modes corresponding 

 usually to some multiple of three. The minimum is also often 

 a multiple of that number. These facts and the sequence 

 of dehiscence of the stamens, the orientation of the super- 

 numerary perianth members, and the frequent occurrence of 

 partially bifurcated organs, suggest that the Ranunculaceae 

 were primitively trimerous, though the feature has become 

 obscured by fission, fusion and abortion. Positive correlation 



