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ON 



1 he Motile r.ea\'es of Mrvthrina Herhaeea 



During a jtai-t nf .Imu'. 191)8. th«' writer was in rcsideiife at 

 the Gnlt' liiulojijc Station. At this time some observations were 

 made on the motile h*aves of Erythrina herhaeea. an iiei-haeeous, 

 ahnost slirnhl)y. phnit l(tcally oecui)\ing moiv or h'ss shady 

 phiees on a hiw ridge near the Statioi] buihling. The ridge 

 was partially eovered with a growth of stunted trees, principally 

 Xantho.xyluni elava hereulis. Crataegus. Bumelia lanuginosa 

 and Celtis mississi|)piensis. The thiekets formed by these trees 

 were sometimes ([uite dari\. though the more usu.il oeeurrence 

 was a more open growth with interspersed elumps of stunted 

 trees. The favorite habitat of Erythrina herhaeea appeared to 

 be the edge of sueh elumi)s. where they reeeived a one-sided 

 illumination. Many plants, however, were found in extremely 

 shaded phiees into whieh direct sunlight never penetrated. It 

 was not common to find tliem in exposed situations. 



Erythrina is mostly a tropical and subtropical genus, the 

 species under discussion being distributed, so far as this country 

 is concerned, through our southern states. 



The leaves of Erythrina are three-foliate, each leaflet bearing 

 a pronounced pulvinus. or motile organ, in common with many 

 Leguminosae. 



^lotility of leaflets is a phenomenon well distrilnited thrt)ugh 

 the Leguminosae and Oxalidaceae. the species varying among 

 themselves in the degree of sensitiveness to light and the rapidity 

 with which they respond to paratonic stimuli. Erythrina is 

 not to be considered in the class with mimosas, sensitive to me- 

 chanical shoek. but rather with thos(^ plants whose leaves respond 

 merely to varying degrees of light intensity. The classic repre- 

 sentative of sueh is the common garden bean (Phaseolus). This 

 plant has long been kufiwn to possess the power of adjusting its 

 leaflets into three dcHnite positions corresponding to the inten- 

 sity of illuniination. One is the so-called sleep position which 

 is assumed in darkness, and in which the leaflets turn so as to 

 point vertically downwards. In this position the spongy paren- 



