160 On the Leaf -arrangement of the Crowherry. [June 15, 



more common forms of leaf-arrangement, in the paper above referred to 

 (Proceedings of the Eoj^al Society, 1874, a'oI. xxii. p.. 298, &c.), and in a 

 " Kote on Variation of Leaf -arrangement," read before the British Asso- 

 ciation at Belfast in August 1874 (see Eep. Brit. Assoc. 1874, Trans. 

 Sect. p. 128). 



Having there drawn attention to two ways in which modification of 

 leaf -arrangement appears mainly to have been brought about — namely, 

 (1) direct variation of numher of vertical leaf-ranJcs, producing the funda- 

 mental orders of different phyllotactic series, and (2) subsequent variation 

 of degree of uniform condensation, eifectiug transition between different 

 orders of the saine series — he now shows (3), from examination of the 

 crowberry, that transition between different orders of different series is 

 brought about apparently by means of unequal condensation resulting in 

 Sjpiral dislocation between adjacent secondary ranks. 



The instrument ( " taxigraph ") used in this research consists of a 

 twig-holder vrhich rotates in fixed bearings, the twig being held in the 

 a,xis of rotation under a framed lens which slides on fixed guides parallel 

 to the twig. Thus the angular position of any leaf is observed by aid of the 

 rotation of the twig-holder, and the vertical position by aid of the sliding 

 motion of the lens. The sliding motion of the lens is conveyed by cords 

 and pulleys to a light frame carrying a strip of paper beneath the plat- 

 form, which is the base of the instrument ; and the rotary motion of the 

 twig-holder is made, by aid of cords and pulleys, to draw a sliding pin- 

 holder to and fro along a slit in the platform at right angles to the 

 direction of motion of the strip of paper below. The pin, in any position 

 of the slider along the slit, is made to pierce the strip of paper on press- 

 ing a lever. Every leaf on the twig is thus observed, and a correspond- 

 ing pin-prick made in the paper. The longitudinal position of any pin- 

 prick shows the vertical position of the leaf, and the lateral position of 

 the pin-prick shows the angular position of the leaf. The whole figure 

 represents the leaf -arrangement of the twig in radial projection, and is 

 bounded laterally by two vertical lines corresponding to one and the same 

 vertical line on the twig. By enlargement of the lateral dimension the 

 arrangement is shown relatively foreshortened. 



The author suggests modifications of this instrument by which it could 

 be adapted to other forms of stem or t^sng; e.g. by causing the paper to 

 rotate under the sliding pin-holder, and by giving the lens a quadrantal 

 motion, it would be adapted to flat or conical systems such as the heads 

 of Compositse. 



The paper was accompanied by the original fifty specimens (less one, 

 lost), and by the fifty " taxigrams " obtained from them : two of these 

 were especially referred to in illustration of the paper. The instrument 

 used was also exhibited. 



