192 PROCEEDINGS OF THE ACADEMY OF [1897. 



of necessity be in the northerly and southerly directions. This is 

 the accepted explanation of this supposed polar arrangement. 



The first blow to my faith in this doctrine was the observation 

 that though the stem leaves have an equal arrangement of stomata 

 on either surface, just as the root-leaves have, they make no attempt 

 at " polarity." Further than this many Australian and Cape of 

 Good Hope plants have vertical leaves, with an equal distribution 

 of stomata on either surface, but there is no polar direction specially 

 to the edges of the leaves. In our own country the leaves of Quer- 

 cus Catesbcei are all vertical the first year from the acorn, but their 

 edges are directed to any point of the compass. It is evident that 

 we must yet regard the question as to the cause of the northern and 

 southern direction of the leaf-edges in the Compass Plant as an 

 open one. 



If we now look over the whole field of Composite, it will surprise 

 us to note how many of this order have the whole or portions of the 

 leaf-blade vertical. Liatris, Lactuca, Chrysopsis, Tanacetum, Cir- 

 sium, Centaurea, Boltonia, Silphium, Mulgedium and Sonclms will 

 furnish numerous illustrations. No one can fail to see that this 

 results from a continuation of the spiral growth into the leaf-blade. 

 In many cases there are two spiral twists in a single leaf blade; the 

 leaves on the flowering stems of these genera are on the \ plan. 

 The epiderm is composed of five leaf bases or dilated petioles as- 

 cending spirally and lapping over each other, and this spiral mo- 

 tion is continued to the free portions which we designate as the 

 proper leaves. This spiral motion is greater in some species than in 

 others. In Liatris it is particularly marked. Not only does the 

 twist become so severe as to turn the leaf-blades strongly on their 

 edges, but extends to parts of the inflorescence. Even the style 

 branches are twisted around each other, and the styles of many dif- 

 ferent florets will coil into a tangled mass. Many other orders 

 besides Composite have the tendency to carry a portion of the 

 leaves vertical, wholly through this richness of spiral development. 

 Onagracerc furnish abundant illustrations ; and the coiling of the 

 leaves of the garden Narcissus must be familiar to many. We can- 

 not consider the condition of such leaves to have any more phy- 

 siological importance than if they had presented a perfectly hori- 

 zontal plane. 



What then is the explanation of the generally north and south 

 line of the leaves of the Compass Plant, admitting, as Ave must, that 



