22 Development of the Fern Leaf 



segments a and b, b obviously will now be at the left side of the 

 base of this rachis if the right one, at the right side. 



If, now, of the two segments at the apex of this rachis, which 

 may be designated as c and d, one (c) becomes transformed into 

 a stalk with two segments at apex, in the same manner as the 

 original simple leaf or segment and as a was transformed, and 

 the other (d) remains undivided, the latter stalk will constitute 

 a second section of rachis which will separate the latter pair of 

 segments from d, while the first section of rachis will still separate 

 d from a. If d were the left one of the segments c and d, d will 

 now be at the left side of the base of this second section of rachis; 

 if the right one, at the right side. D and b may, therefore, be 

 either on the same side of the rachis composed of the two sections 

 or on opposite sides. If on opposite sides, they will be alternate, 

 since they will be separated by the length of a vein. This vein 

 may, however, be so short as to be imperceptible to the naked 

 eye, in which case they will appear opposite. 



If, instead of the segments subdividing in the above-described 

 order, the original simple leaf-blade or segment becomes trans- 

 formed into a stalk with two segments at apex, in the manner 

 above described (i.e., by subdividing into segments and becoming 

 attenuate below these segments), and each of the latter segments 

 becomes transformed likewise into a stalk with two segments at 

 apex, a dichotomous rachis with two segments at each end of its 

 fork will result; for this reason. The starting-points of the two 

 segments formed by the subdividing of the original simple leaf- 

 blade or segment will also be the apex of the stalk composed of 

 the lower part of the latter; hence, when the lower parts of these 

 segments shall have become stalks, the starting-points of the latter 



