74 CARNEGIE INSTITUTION OF WASHINGTON. 



divided with linear or thread-like divisions. It seemed to offer suitable 

 material for a test of the extent to which the ontogenetic procedure of 

 a plant might be altered by environment, the degree of functional 

 adaptation shown by these changes, and also to promise some evidence 

 upon the nature of regenerative changes which precede reproduction. 

 Cultures under controlled or measurable conditions have been carried 

 on in the New York Botanical Garden, at Cinchona, Jamaica, and in 

 the various plantations of the Department since 1903. The results 

 obtained under these temperate and tropical, moist and arid, mountain 

 and seashore climates, and in aquatic and terrestrial habitats, in a 

 decade may be briefly summarized as follows: 



The cultivation of Neoheckia as a terrestrial was accompanied by 

 the development of thickened roots, in which an exaggerated formation 

 of cortical and fibro-vascular tissues ensued. Large amounts of starch 

 accumulated in these members, the entire reaction being one which 

 probably does not occur in nature. Variations in the form of nepionic 

 leaves have been seen coupled with the composition of the medium or 

 substratum, with the availability of a supply of food to buds, and with 

 competitions. No connection was established between the form of 

 such organs and the stage of the material taken for rejuvenescence, 

 although in most of the experiences such effects would have been 

 masked by other effects. While it is true that most of the diverse 

 structures exhibited by the leaves of Neoheckia show some degree of 

 suitability to the conditions under which they are formed, yet this is 

 by no means always the case, as instanced by the occurrence of terres- 

 trial tj^pes in submerged plants. This of course is still more notice- 

 able in the various regenerative proceedings in which the form and 

 structure of the leaves are determined by the presence or abundance 

 of certain formative materials. The form and structure of roots and 

 foliar organs of Neoheckia are seen to be determined by environic 

 conditions to a much greater extent than in Proserpinaca, Siiim, or 

 probably any other so-called ''polymorphic" species, yet the reaction 

 to such external agencies is not a direct or physical adjustment, and 

 is purely directly resultant. The full detail of this work is given in 

 Flora, vol. 106, pp. 265-280, 1914. 



The Role of the Factors of a Desert Complex in Evolution Processes of 

 the genus Leptinotarsa, hy W. L. Tower. 



The chief point of interest in the investigations at Tucson during 

 the past year concerns the further study of the series of mutating stem 

 stocks produced at Tucson, through the hybrid sj^nthesis of two or 

 more parent species into one invariable form. These, as described in 

 previous reports, remained stable and did not break up, according 

 to the recognized principles of hybrid reactions, and continue to remain 



