MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 261 



this plant consisted in the exaggerated development of the paren- 

 chymatous tissue in the center of the stelar tract, between and in the 

 bundles. No definite trace was observed of a layer approximating 

 the special pericycle found by Bonnier in the etiolated petioles of 

 hellebore, however (see p. 28). The laminar portions of the com- 

 pound leaves of Pastinaca failed to develop in darkness and remained 

 in small clumps with but little differentiation of tissue. The basal 

 portion of the leaf showed an excessive elongation and this growth 

 was shared to some extent by the midrib, but not by the branches of 

 the midrib. Consequently the divisions of the leaf were held farther 

 apart than in normal leaves. The ultimate amount of growth that 

 might be accomplished b}^ any etiolated leaf seemed to be increased if 

 concurrent organs arising from the same axis were removed. The 

 duration of the etiolated leaf was comparatively brief, and the under- 

 ground axis perished soon after the leaves. The cauline leaves of 

 PodofhyUum developed leaves in darkness with petioles much in 

 excess of the normal (about 80 per cent.) but the laminae accom- 

 plished but a fraction of their normal superficial expansion. Stomata 

 were not differentiated, and the leaves were of comparatively brief 

 duration. Flower-bearing stalks bore leaves which had similar rela- 

 tions to darkness, but were slight!}' less differentiated. Etiolated 

 leaves of Potentilla also had unusually elongated petioles and showed 

 but little growth of the laminar portions. The reactions of Rheum 

 and Riimex presented certain features in common. Both forms pro- 

 duced greatly elongated petioles in darkness, and made an excessive 

 growth of the prolongation of the petiole in the lamina. The growth 

 of the ribs of etiolated leaves of Rhcwn did not exceed the ultimate 

 dimensions of normal leaves, but the laminae developed much more 

 slowly and to a limited extent, so that the latter were torn and rup- 

 tured in many places by their inability to expand in the usual manner. 

 The petiole of Ritmex was developed to an excessive length, and 

 the midrib also showed an abnormal growth which ruptured the 

 feebly growing lamina. In this species the lamina was often suffi- 

 ciently tenacious to set up a tension with the midrib by which it was 

 held in a curved position. The leaves of both Riimcx and Rheum 

 were of comparatively brief duration although the former were fur- 

 nished with functional stomata. A succession of etiolated organs 

 was produced by Riiniex during a period of several months. Viola 

 obliqua developed etiolated leaves with petioles about double the 



