594 RECORD OF CURRENT RESEARCHES RELATING TO 



fourth it is proved that free oxygen is essential to heliotropism, and 

 that all holiotrojiic curvatures are dejjeudeut on unequal growth. 

 The fifth and last chapter treats of photo-mechanical induction in 

 heliotropism ; the important fact being here demonstrated that the 

 inductive actions of light and gravitation do not cooperate, but are in 

 opi)osition to one another, and that heliotropic induction is virtually 

 mechanical.* 



Symbiosis.f — Professor L. de Bary, in his address at the last 

 Meeting of German Naturalists, proposed the term " symbiosis " 

 as a general designation for parasitism and analogous phenomena 

 (" mutualism," &c.) in the vegetable kingdom, for which the terms 

 used in zoology are not always exact or appropriate. He distinguishes 

 two j)rincipal divisions — " antagonistic symbiosis," in which there is 

 a struggle ; and " mutualistic symbiosis," in which the two organisms 

 receive a reciprocal advantage. 



Is the Ovule an Axial or a Foliar Structure ? J — The theory that 

 the ovi;le is of the nature of a bud was powerfully upheld by the great 

 morphologist, Von Mohl. Of recent years the opposite view, that it has 

 more the character of a leaf or of a part of a leaf, advocated with great 

 weight of ai'gument by Celakovsky, and finally supported by Eichler, 

 has met with favour from the majority of botanists. Great ingenuity 

 has been disj^layed on both sides in adapting to each theory, facts 

 which appear at the first sight plainly to contradict it, especially in 

 the case of malformations, on which both j)arties greatly rely to prove 

 their case. 



Under the title " Ueber Placentarsprosse " Peyritsch supplies 

 another contribution to the literature of the subject. He starts with 

 the assertion that cases, in his opinion, unquestionably occur, of 

 placental shoots or buds taking the place of ovules, with regard to 

 which there is no reason for regarding them as adventitious shoots. 

 This view he supports by the description of abnormal placental struc- 

 tures in Besecla lutea, Sisi/mbrium AlHaria, and other cases. He 

 believes that neither of the two rival theories can be accepted as of 

 universal apidication, but that a series of intermediate forms exists 

 between the normal ovule and the nucleus-bearing segment of a leaf. 

 Notwithstanding all that has been said to the contrary, the normal 

 ovule has more the characters of a bud than of a leaf, and can best 

 be compared to a minute bulb, while malformations often partake 

 much more of a foliar character. He regards, therefore, the ovule as a 

 structure adapted for sexual reproduction, of a variable morphoL)gical 

 natiire, and is not of opinion that abnormalities are of any great value 

 in determining this last question. As an analogical structure he 

 adduced the cyathium of the Eui^horbiacete, intermediate between an 

 inflorescence and a true flower, and regarded by the best authorities 

 in dificrcnt lights. 



* See 'Bot. Zeit.,' xxxvii. (1879) p. 341. 

 t 'Eev. Internat. Sci.,' iii. (1879) p. 301. 

 J 'SB. Akad. Wi.ss. Wieu,' Ixxviii. (1S7S) p. 220. 



