Bu r US and H edd e n , Conditions iiifluencing regeneration of hypocotyl. 391 



In all these cases there is a liindrance to the normal move- 

 ment of materials in the plant — organs whicli normally function — 

 have ceased either entirely or partially to do so, in one case 

 from internal, in the otliers from external causes. That is, the 

 prodiiction is due to correlation and not to the wound. 



2. The experiments contirm the Observation of Goebel^) 

 that embryonic tissue reacts easier than old tissue. The young 

 hypocotyl is apparently able to prodnce a bud from every part 

 of the epidermis. This ability gradually is lost as the plant 

 gets older. In old plants however, this ability is retained by 

 the part nearest the base, that is the oldest part of the hypocotyl. 

 This part is especially predisposed to produce buds. Even in 

 the young plants the first bud usually appears nearer the base 

 than apex of the hypocotyl of decapitated seedlings. 



It was not determined whether or not any special cells in 

 the epidermis differed from others in complexity of structure or 

 amount of protoplasm contained as is the case in certain leaves.^) 



3. Polarity. Decapitated seedlings do not show polarity. 

 The origin of the first buds in many cases is toward the base 

 of the hypocotyl. The origin of the bud at base of the old 

 plant confirms this also. 



Unter the paragraplt on light however, we saw that „pola- 

 rity" became very niarked in Linuni when the upper part of 

 the decapitated seedling was strongly illuminated. Without light 

 and a relatively streng light, regeneration did not take place. 



The fact has been noted in other cases that buds were 

 produced only on the light side. On the other hand Horn- 

 schuck thinks that weakened illumination may be a factor in 

 the development of buds on leaf of Malaxis paludosa, a Suggestion 

 with which Goebel does not agi-ee.^) 



In many cases Goebel*) has pointed out the relation of 

 the place of origin of „adventitious" buds to the fibrovascular 

 bundles. This is seen in case of Begonia Rex, Utricularia, Car- 

 damine pratensis. (See illustration.) 



The facts observed on seedlings with the light experiments 

 seem to run parallel with these. The bundles are the places 

 through which material is moving. In our young seedlings the 

 bundles are not well developed. When however, the cotyledons 

 are removed or cease to function, their work is taken up by the 

 epidermis. The cells of this develop a vast amount of Chloro- 

 phyll and all movement is to and from them. Very soon after 

 they originate one or more are connected with the conducting 

 System, the others })erisli. Only those cells exposed to light, 

 function as the cotyledons and hence all flow of material is to 

 and from the lightest side. Light is then an indirect cause of 



1) Goebel, Über „Regeneration im l'llanzenreicli". (Biol. Centralbl. 1902.) 



Willkürliche lOiitwickluiigsänderungeu bei Pflanzen. Jena 1903. 



2) Klebs, Regenerationen bei Utricnlaria. Bd. 93. p. 118. 



3) _ Flora. 93. p. 11 H. 



4) Biol. Centralbl. Flora. 93. etc. 



Beihefte Bot. Centralbl. Bd. XIX. A>.t. I. Heft 3. 27 



