Roberts and Struckmeyer — 95— Anat. and Histol. Changes 



The induction of sexual reproduction by grafting a flowering plant 

 upon a "receptor" plant has been reported by a number of workers (3^, 7, 8, 

 10, 41). When plants are brought to flower by the grafting technique the 

 receptor plants exhibit anatomical changes similar to those induced to 

 blossom through photoperiodic conditions, temperature or age. 



Two other lines of evidence show a correlation of anatomical structure 

 with sexual reproduction. One is the characteristic amount of phloem 

 tissue in a species and the other is the renewal of cambial activity when 

 plants which are in flower are made to produce new vegetative shoots (34). 

 Its significance is not known but it is very suggestive of a common physio- 

 logical basis for sexual reproduction that several species of plants which 

 blossom early and continuously in a very wide range of environmental con- 

 ditions as buckwheat {Fagopyrum esculentum) were found to have a very 

 Hmited amount of phloem tissue (37) ; also, that other species which can 

 rarely be induced to form blossoms as commercial varieties of sweet potato 

 (Ipomoea batatas) had a characteristically abundant formation of phloem. 



The renewal of cambial activity after the induction period as in cases 

 like the unilateral production of xylem cells resulting in the large-diameter 

 spurs characteristic of the apple when blossom buds are developing, the 

 growth of perennials after a rest period or the return to active cambial 

 formation when plants are replaced in an environment unfavorable to 

 blossom initiation (34) will not be considered now. Neither will a dis- 

 cussion of the questions arising in connection with late bud development, 

 flowering, fruit set and fruiting be undertaken. Conditions most conducive 

 to induction are of course often very different from those giving optimum 

 fruiting in a commercial sense. 



Literature : — There are rather numerous references to the effects of 

 photoperiod or other external environmental factors upon stem anat- 

 omy (9). As the plants have been sampled according to the cultural 

 treatment and not the reproductive state, it is not usually known but can 

 only be guessed as to whether the anatomical condition observed bore a 

 relation to blossom initiation. An example is Hamner's statement (6, 

 p. 586) : ". . . . PsAREV et al. found an increased cambial activity during 

 induction." 



The papers by Psarev (12, 13) and Psarev and Neuman (14) which 

 Hamner cited do not record the cambial activity nor do they describe the 

 cellular structure either during induction or at a later time. They report 

 only an increase in stem diameter of mature soybean plants grown in short 

 days (presumably due to longer continued cambial activity.) The short 

 day plants of Psarev (14) had some internodes which "assume a shape 

 of abnormal swellings or 'tumors' which look like those induced by several 

 different authors through treating the plants with growth substances." From 

 this fact and also the statement that mature plants in short days averaged 

 only 10.2 and 15.6 cm. in height, it appears that Psarev was working with 

 abnormal plants such as occur in short days in the greenhouse when the 



' It is suggested that inexperienced workers take care to use correct temperatures 

 when experimenting with Hyoscyamus niger as this plant appears more responsive 

 to different levels of temperature than to long or short photoperiods. 



