Rosaceæ. 7 



The figure given of the structure of the shoots of Poten- 

 tilla palust., illustrates a common feature as regards the shoot- 

 succession when flowering begins. After the winter-bud, 

 which is shown by the short internodes, the first 2 — 3 elon- 

 gated internodes of the floral shoot form a continuation of 

 the older axis, while the following internode constitutes the 

 basal part of the ascending branched floral axis. Often even be- 

 fore flowering begins the principal bud grows out, subtended by 

 the leaf (Fig. l,c) which is seated at the base of the flower-stalk, 

 and forms a sympodial continuation of the axis. But different 

 specimens from the same locality, at any rate in Denmark, 

 may differ greatly as regards the degree of development 

 reached by the principal shoot during the year in which the 

 parent-shoot flowers, in that the length may vary from 2 cm. 

 to about 10 cm., and this proleptic development is by no 

 means a fixed rule even though it is certainly typical in tem- 

 perate regions. By comparison of herbarium specimens from 

 Denmark, Iceland and Greenland in the Botanical Museum in 

 Copenhagen, it appears, however, to be the rule that the pro- 

 leptic development of the principal shoot is rarer in the two 

 latter countries than in Denmark, and rarer in Greenland 

 than in Iceland. It was found to be the rule among the Green- 

 land specimens that the principal bud did not emerge until 

 next spring. In vigorous specimens from Denmark, the leaves 

 a and b in Fig. 1 also often subtend proleptically developed 

 supplemental shoots ("Bereicherungsschüsse") while such were 

 not found in the Greenland specimens in the herbarium, and 

 in only a few of those from Iceland did the leaf b subtend 

 a slightly precocious shoot. This proleptic development may 

 perhaps be regarded, for instance, as a weapon in the struggle 

 against the mosses among which Potentilla palustris commonly 

 grows; since if the growth in length of the obliquely placed 

 stem was arrested in the middle of summer by the formation 

 of the floral shoot it might easily be overgrown by the mosses. 



