202 THE QUANTITATIVE METHOD IN BIOLOGY 



(2) The length of the sheath of the successive leaves taken in 

 the same order ; 



(3) The length of the blade (lamina) ; and 



(4) The breadth of the blade of the successive leaves 

 (measured at the place of their greatest breadth) . 



The figures are given in the following Table : 1 



Gradation in a flowering stem of Holcus mollis. Four priraordia have been meas- 

 ured : length of the internodes, length of the sheaths, length and breadth 

 of the blades of the leaves. The internodes are numbered (I., II., . . .) from 

 the base to the summit. The figures of each leaf are in the same vertical 

 column as the figures of the internode at the base of which it is inserted. 

 The limit between the stem and the inflorescence is indicated by ] [. The 

 lowest leaves were faded and could not be measured exactly. Dimensions 

 in mm. 



With regard to the length of the internodes the remarks made 

 about Poa (first example) are also applicable to Holcus. Here, 

 however, the humps observed in the internodes II. and XI. 

 seem to be something more than fortuitous deviations. We 

 know that the internodes I. -XVI. (stem properly so called) 

 have been formed successively in acropetal order ; therefore 

 they represent a period of growth. In the course of this period 

 something has happened by which the regular progress of 

 growth has been disturbed two times : this has produced two 

 secondary humps (internodes II. and XL) in the gradation 

 curve. In other words, several secondary waves of growth 

 have followed each other. 



I have observed similar facts in the fertile stems of certain 

 Mosses.^ In Mnium subglobosum and Mn. punctatum, two 

 waves occur rather frequently in the ascending portion of the 

 gradation curves (length and breadth of the leaves). Here the 

 limit between the waves is more conspicuous than in the above 

 bertilloned^ stem of Holcus', it is really a distinct breach of 



^ A similar example is given in my paper on Mnium, p. 14, Fig. 3. 



2 See p. 33 in my paper on Mnium mentioned in the present book on p. 69. 



^ From the French verb bertilloner. See note 2, p. 201. 



