Roberts and Struckmeyer —97— Anat. and Histol. Changes 



arise.) Several species which produce blossoms at any node have been 

 readily induced to flovi^er by the grafting technique. 



The blossoming habit of the plant should be considered when "trans- 

 fer" experiments are being planned. It should also prevent unjust criti- 

 cisms being made such as have begun to appear in the literature, when two 

 workers obtain different results, obviously from the use of plants of differ- 

 ent flowering habits. 



After- Affect : — Another phenomenon which varies with the flower- 

 ing habit of the species is the difference in reaction to a change in environ- 

 ment, after the plant has come to flower. Plants with a terminal flowering 

 habit as Klondyke cosmos, poinsettia, Rudbeckia laciniata, Salvia (var. 

 Harbinger), stock (Qiristmas Pink) and Maryland Mammoth tobacco 

 can be readily changed to a vegetative state after they have come to flower 

 by placing them in an environment which inhibits flowering. Plants with 

 a systemic flower forming habit as morning glory (var. Heavenly Blue), 

 petunia (forcing), soybean (var. Biloxi), and Xanthium echinatum do not 

 revert to a vegetative growth cycle in a reversed environment, once they 

 have come to flower and fruit. 



The continued flowering of an induced plant after being transferred to 

 an environment unfavorable to flowering (provided it is of a species hav- 

 ing a systemic blossoming habit) presents an interesting problem. The 

 mechanism of the "after-affect" has been the subject of considerable theoriz- 

 ing. A possibility of an effective mechanism is presented by the fact that 

 annual plants which show after-affects do not characteristically renew 

 cambial activity once it has ceased at the time of induction and flower- 

 ing (34). In this connection it must be kept in mind that plants which 

 require a long period of treatment to establish a permanent after-affect will 

 revert to a vegetative type and regenerate cambial activity if the induction 

 treatment is discontinued before induction is completed. Terminally flow- 

 ering varieties regenerate cambium whenever returned to an environment 

 unfavorable to blossom induction. 



Monocotyledons : — An extensive study of the relation of stem anatomy 

 to flowering of monocotyledons has not been attempted as so few of the 

 commonly available species have stems suitable for sampling when in a non- 

 flowering state. The grains and grasses as well as most other locally grown 

 species of this group are in an induced state before stems long enough for 

 sampling of internodes are produced. 



Histology : — Too little original work has been done on the question 

 of the relation of plant composition to blossom induction to be of much 

 significance. It is of interest that the etiolated type of plants grown in 

 warm nights and cool days may have so little carbohydrate that no starch 

 and almost no free reducing substance is found by qualitative tests. 



Consistent differences in the mineral pattern of flowering and non- 

 flowering stems have been found (35) . It has also been repeatedly observed 

 that a change in the mineral distribution becomes apparent very soon after 

 plants are placed in an environment inducive to flowering. A changed 

 pattern is evident in as short a time as two to three days in some species 

 (Figs. 7, 8, opposite p. 95). 



