126 



SCIENCE- GOSSIP. 



Witches' Brooms. — I presume our Botanical 

 Editor, in his reference to the scanty English 

 literature on this subject, excluded English trans- 

 lations of German works wherein witches' brooms 

 are referred to, but to those interested in this 

 subject these translations are of value. These 

 aberrations are mentioned in " Comparative 

 Morphology and Biology of the Fungi," by De 

 Bary ; " Diseases of Plants induced by Crypto- 

 gamic Parasites," by Tubeuf and Smith ; and 

 " The Diseases of Trees," by Hartig, English 

 translation by Somerville and Marshall Ward. 

 The phenomenon is not alone caused by species 

 of the Uredineae, but the Ascomycetes are also 

 responsible for some. Thus Exoascus deformans is 

 responsible for the witches' brooms on Perslca 

 vulgaris, Amygclalus covimunis, Prvnvs avinvi. 

 P. eerasus, and P. domestica; Exoasciis insititi ae- 

 on Prvnvs insititia ; E. carpini on Carpinns ietulus, 

 and, I regret to say, many of them are to be met 

 with frequently. — Carleton Pea, B.C.L., M.A., 

 34 Foregate Street, Worcester. 



STRUCTURAL and PHYSIOLOGICAL BOTANY. 



conducted by harold a. haig. 



Torsion op Leaves in the Douglas Fir. — 

 With regard to the orientation of leaves, having 

 as a result the turning of the assimilatory surface 

 towards the incident rays of light, a well-marked 

 instance occurs in Ah'ws dovglasll (fig. 1, a). 



Position assumed by leaf 

 in nature (arrow indi- 

 cates direction of inci- 

 dent rays). 



Position wliicb would 

 be assumed if there 

 were no torsion. 



At a point close to where the leaf springs from 

 the main axis there occurs a twisting of the leaf- 

 base (see fig. 1, a;), which results in the bringing 

 of the dark-green upper or dorsal surface of the 

 leaf to lie in a plane that is best calculated to 

 receive the optimum intensity of light. The several 

 leaves of one side of the main axis belong to 

 different spiral whorls, but it may be seen that 

 they are disposed in rows alternately one above 

 the other, so as to lie in separate planes which cut 

 the axis inclined at various angles to the trans- 

 verse median plane. By this method every one of 

 the leaves receives a definite amount of light, 

 those most anterior receiving light at the greatest 

 obliquity of incidence ; those most posterior getting 

 light of nearly vertical incidence. 



French View of the latent Vitality of 

 Seeds. — M. Armand Gautier, in the " Revue 

 Generale de Botanique," writes on this subject and 

 says: — "A perfectly dry seed, a bacterium or its 

 spore, or a rotifer deprived of water, all possess a 

 fit organisation for the seat of life-processes ; but 



they do not live in the true sense of the term : 

 their life is latent \j^le latente']. Functionally 

 speaking, life means assimilation. . . . They only 

 become the seat of the manifestations which con- 

 stitute life when the determining causes, moisture, 

 warmth, and an initial im^julse furnish them with 

 the necessary conditions for realising the vii-tual 

 energy which their chemical constituents hold in 

 reserve. That a certain number of seeds lose after 

 some years the power of germination is the natural 

 consequence of the fact that the chemical prin- 

 ciples which compose them are in a state of 

 tension with regard to potential chemical energy. 

 These chemical principles are slowly modified, 

 and there is nothing to show that this modi- 

 fication is a form of the vital function." M, 

 Gautier is evidently of the of)inion that it is a 

 species of " potential chemical energy " that gives, 

 to seeds their power of responding to external 

 influences, and that all that is required to convert 

 a given seed into an active element is an initial 

 impulse, with the essential surrounding conditions, 

 of warmth and moisture. What does he mean by 

 ■' initial impulse " ? Surely it depends upon those 

 very conditions, and is not a thing to be spoken of 

 apart from them. It is, one would think, a little- 

 difficult to accept M. Gautier's explanation of the 

 loss of vitality of seeds. Modification of the- 

 chemical principles of the protoplasm argues a 

 rearrangement of the molecules composing it ; but 

 there has been no proof yet of any such modifica- 

 tion. We believe that Dr. Waller's experiments- 

 upon the " blaze-reactions " of living seeds which 

 were mentioned in a jDrevious paragraph (S.-G.,. 

 ante, p. 31) throw much light upon the under- 

 standing of this interesting problem. 



Isolated Elements in Leaf of Araucaria. — 

 There is an interesting instance of the deposit of 

 raphides, or crystals of calcium oxalate, in the 

 walls of certain elements in the case of some thick- 

 walled, irregularly shaped cells that are to be 

 found scattered throughout the leaf of Araucaria. 

 We find at certain parts of the mesophyll large 



Fig. 2. Largk '['hick-walled cell from leaf of 

 Araucarfa excelsa. 



a. Cell of the spongy parenchyma, r. Tliick-walled element ire 

 the WciUs of which " raphides " have been deposited. /. Lati- 

 ciferous cell. r. Raphides. 



stellate elements with rather thick walls, which 

 latter ha^'e deposited in them numerous smalB 

 crystals, rhombic in form, that can be seen to 

 extend throughout the whole thickness of the- 

 wall, and even deposited on the outer surface (see 

 fig. 2). These isolated elements are surrounded 

 by the ordinary large colls of the spongy paren- 

 ciivma, and have in their vicinity an occasional 



