(;9^! 



Kui'i'KK : Anatomy and Physiology 



of the leaf-base, named b}^ Vines the " hypopodium." Their pe- 

 culiar phyllotactic arrangement would thus obviously be explained. 

 The question was raised however as to whether these facts alone 

 /. c, the connection with the leaf-base and their phyllotactic rela- 

 tion, would be sufficient to establish the homology with leaf- 

 structures. The point was decided in the negative for the follow- 

 ng reasons : 



I. Their main axes, even at the growing point, are parallel to 

 the stem, instead of at a greater or less angle as in other developed 

 leaf-bases, /. c, stipules. 



Fk;. 9. Cross-section of wing 

 of Baccharis genistelloides. 



Fig. 10. Cross-section of leaf 

 of Baccharis gaiistclloides. 



2. In many plants, Latliynis latifoiia, L. sylvcstris and L. 

 grmidiflonis among others, both stipules and wings occur. In 

 such cases the wings, although just as obviously continuous with 

 the wings of the petiole, evidently could not be hypopodia. 



3. Other organs have been found that follow the leaf arrange- 

 ment, but may not therefore be supposed to be leaf-structures — 

 for example the thorns in some species of Riibus and Siiii/ax, the 

 ridges in the stems of Urtica gracilis^, McntJia crispa and Lcptandra 

 Virginica. 



For these reasons the wings are, it seems to me, rather to be 

 regarded as lateral-vertical expansions of the stem than as " decur- 

 rent leaf-margins." 



Phototropism 



To determine the action of the plant towards light a growing 

 shoot was fastened in a dark chamber illuminated from one side 

 only. After fourteen days there was found to be a decided photo- 



