X909 ] LEAVITT—HOMOEOSIS IN PLANTS 49 



the pinnae, and resulting in the formation of segments of a second- 

 ary rank imitating the normal primary segments; and further, in a 

 change in spacing of the divisions, which brings the modified pinnae 

 into conformity with the main frond-plan as regards the distance of 

 the segments. Increased spacing, correlated with perfected divisions, 

 in very obvious homoeosis, is also seen in Osmunda cinnamomea 

 (Jig. 13) collected by F. G. Floyd at Mt. Desert, Me., where, accord- 

 ing to the collector, the form is evidently hereditary, numerous modi- 

 fied plants covering a considerable area. 34 



Coming to flowering plants, the principle is seen in curious varia- 

 tions of the leaves of an Aster which Mr. C. Stuart Gager has 

 kindly shown me. They were briefly noticed by him in Torreya for 

 January, 1908. Basal laciniae have become increasingly distinct, 

 some of them even petiolate (petiolulate) ; and when so, the new, or 

 secondary, blades imitate the main blade, even down to a peculiarity 

 of asymmetrical development. 



I regard a leaf condition found by me in Gleditsia triacanthos 

 as homoeotic. At any rate the variation noted is very abrupt. The 

 character leaf of the species is simply paripinnate, the leaflets short- 

 stalked, the blade slightly unequal at base, elliptical, obscurely ser- 

 rulate or crenate, apiculate. In the leaves of vigorous running shoots 

 (not spur shoots) I find some of the leaflets replaced by segments 

 imitating the normal leaf in all the features specified above; the 

 segments are, in effect, character leaves of a second order. The 

 modified, or compound, leaflets, which are nearly twice as long as 

 the unmodified ones, occur irregularly among the others (fig. 14). 

 The condition here, essentially the same as that described for the 

 Person fern, has been noticed also by Gager (I. c.) , one of his 

 specimens— as also one of mine— carrying the homoeosis to the 

 second degree, a few pinnules becoming perfectly compounded (as 

 in the Whitman fern). There is no evidence, so far as I know, that 

 L! modified condi tion looks back to an older, normal state of division. 

 i ^at happens is that segments of the leaf are transformed into the 



eness of something now existing— the normal, or character, leaf of 



lik 



ferns * f™ m?hs of tropic homoeosis may be found i 

 . ^reat Britain, etc.. Nature ™; n ^A t ~„^„ , 



Moore 



Drint..i * Brita »», etc., Nature printed. London. 1857; and in Moore 

 P^ted Brmsh ferns. London, r 859 ( ?). 



Mo " *ot Garden 



1909 



