1889.] NATURAL SCIENCES OF PHILADELPHIA. 55 



is a comparatively recent stage in evolution, wherein a geotropic 

 stem has assumed an erect condition. 



Again, the author does not know that it has been so recorded by 

 phyto-biological authors, but growth in plants evidently follows the 

 law that prevails in most forms of motion, and is rhythmic and not 

 continuous. Rest and activity follow in rapid succession as the 

 parts of a plant grow. It is during these various stages of rest and 

 activity that the successive morphological changes take place. It 

 is probable that during these resting spells, the changes in the tor- 

 sional direction occur. It has been shown by the author of this 

 paper (see Proceedings of Academy, 1886, page 291) that after the 

 resting spell that follows the expansion of some malvaceous flowers, 

 they take the opposite direction in twisting as they close. The 

 plants there noted are annuals, and the inflorescence is not secund. 

 The alternate twists are in contrary directions, during successive 

 resting periods in the same flower. 



Noting that in an allied order a member, Mahernia verticilfata 

 had secund flowers, it was thought probable the expanding 

 corolla itself, might show alternate twisting in contrary direc- 

 tions. This proved to be the case, the lower flower of the two 

 twisting against the sun, and the upper with the sun. Fig. 2 rep- 

 resents a front-face outline, showing the opposite direction 

 ^""^ of the twists in the two flowers of the common) peduncle. 

 J Notwithstanding the flower does not expand to the extent 

 the malvaceous plants referred to above do, and the con- 

 sequent difficulty the separate petals must have in changing 



the over-lap in fading, yet numbers succeed, showing that 

 Fig 2 



here also the return spiral twist is in a different direction 



and is not a mere coiling up of the same expanded spiral chain. 



Distinct spiral directions in the growth of branches on the same 

 plant have been occasionally noted (see Goodale Bot. Text Book, 

 p. 407). The object of this paper is to show that it is very common 

 in the inflorescence, and that it is indeed the cause of that section 

 known as secund. The author would show that the inverse of Dr. 

 Gray's definition of a stolon may be accepted. He says, — " A 

 stolon is a prostrate or reclined branch which strikes root at the tip, 

 and then develops an ascending growth, which becomes an inde- 

 pendent plant." We now see that the stolon itself, with its unilateral 

 arrangements, may again ascend and become a branch. 



