120 



Koellia flexnosa (Walt.) MacM. ; Sanguisorba Canadensis L.; 

 Poly gala viridescens L.; P. verticillata L.; Rhexia Virginica L.; 

 Dipsacus sylvestris Huds.; Baptisia tinctoria (L.) R. Br., nearly 

 out of flower ; Ciiscnta arvensis L.; Spiraea salicifolia latifolia 

 Ait.; Iva frutescens L.; Panicum virgatum L.; Rynchospora 

 glomerata (L.) Vahl and Apios Apios (L.) MacM. — S. H. B. 



REVIEWS 



The " Peg " or " Heel" in Seedlings of the Cucurbitaceae 



For many years that curious adaptive structure known as the 

 " peg " or " heel " which serves to open the seedcoat in seedlings 

 of the cucurbits has been an object of study for many investiga- 

 tors. The extent to which this has been the case is indicated by 

 the extraordinary number of papers which have been devoted to 

 it, namely 531 ! 



The last of these is from the laboratory of the Agricultural 

 Academy at Bonn, by Professor F. Noll.* The very interesting 

 and important results of the investigation are given below in the 

 form of a partial translation : 



As shown by Darwin, the structure in question is produced 

 at the point of union of hypocotyl and root. Its lower half 

 is therefore morphologically root, and the upper half stem. 

 Qualitatively, the axis at this point is able to produce the peg 

 on all sides. On the broad flanks of the axis, which in transverse 

 section is elliptical, the peg develops more strongly than on the 

 narrow flanks. Quantitatively, therefore, the axis differs in this 

 regard in different regions of the sensitive zone. 



The development of the peg, which is for the greater part con- 

 fined to one side of the axis, occurs in response to two kinds of 

 stimuli. 



1. Its localized origin is on the one hand dependent on the 

 stimulus of gravitation, and is formed on the under side. By re- 

 versing a sufficiently young seedling, a second peg may be called 

 out on the opposite side. 



* Zur Keimungs-Physiologie der Cucurbitaceen. Landwirtschaftliche Jahrbiicher. 

 1901. 145-165. Erganzungsband I. 



