1890.] NATUKAL SCIKNCKS OF PHILADELrillA. 277 



Larcli or the regular Pine needles. Having no axis to adhere to, these 

 true leaves in the Norway Spruce seem to grow the larger by reason 

 of their freedom. In some cases these leaves from the bud scales are 

 large enough to simulate those at the apex of Sciadopitys, and give 

 the same parasol-like appearance to a spruce branch. 



The chief point of this paper is to call attention to the direction 

 of the spiral or twist of these free leaves. Along the central stem, 

 as already noted, the free leaves are usually on a line parallel with that 

 stem, but occasionally they twist to the right or to the left. The 

 same is true of those of the buds. They nearly all twist one way or 

 other. As the adult leaves around the stem all coil in one direction, 

 one might reasonably expect the free leaves to do the same. It is 

 surprising to find that they frequently do not, as many will be found 

 on the same plant twisting in either direction, though every leaf in 

 the same bud has the twist in the same direction. 



Attempts have been made to explain the law underlying the spiral 

 arrangement of the leaves of plants. The indifferent directions 

 taken by the leaves of the Norway Spruce, as detailed, would indi- 

 cate that, whatever that law may be, it is rather local than in con- 

 trol of the whole system governing the growth of the plant. 



