610 SUMMARY OF CURRENT RESEARCHES RELATING TO 



most important change which the epiderm undergoes as the result of the 

 action of the gall-irritant is the formation of hairs. 



In the fully developed gall itself, the epidermal tissue is principally- 

 developed as epiderm ; cork and bark are rare. The stomates of galls 

 are often developed as air-fissures which remain permanently open ; in 

 some willow-galls true lenticels are formed. The assimilating tissue is 

 usually but feebly developed ; mechanical tissues are almost invariably 

 present in those galls which are produced by growth in thickness. No 

 stereids are present. 



The cells of galls may resemble in form and arrangement those of 

 the normal parts of the plant ; or the arrangement may be changed ; or 

 forms of cells and tissues may occur which are not present in the normal 

 parts of the plant. The gall-irritant is a compound of various sources 

 of irritation. 



Seasonal Dimorphism.* — Prof. E. v. Wettstein refers to the occur- 

 ence of tliis phenomenon in the vegetable, as in the animal kingdom, 

 and regards it as a potent factor in the evolution of new species. As an 

 instance he alludes to the changes introduced into meadow and pasture 

 plants by the annual cutting of the grass ; by which, in such genera as 

 Gentiana, Euphrasia, Bhinanthus, Galium, Campanula, &c, the species 

 are divided into two sections, — those which ripen their seeds before the 

 mowing, and those which do not blossom till after the mowing. 



Influence of Animals on Plant-life.f — Herr E. Ule records examples 

 from the Tropics of various modes in which animals assist in the repro- 

 duction, the distribution, or the protection of plants under the following 

 heads : — Bats as distributors of seeds (a species of Cecropia) ; Leaf- 

 cutting ants as carriers of seeds (Ipomsea pes caprse) ; Small ants 

 protecting plants against the attacks of leaf-cutting ants ; Petals as food- 

 materials for insects and birds ; Extrafloral attractive organs as signals 

 for fructivorous animals; Wholesale visiting by Insects with no result 

 as to fertilisation (palms, &c). 



Embryo of "Mummy" Wheat and Barley.}— M. E. Gain has 

 examined the structure of the embryo of grains of wheat and barley 

 obtained from Egyptian mummy-cases, and finds that, although the 

 external appearance of the grain is unaltered and the reserve sub- 

 stances have maintained their chemical constitution, the embryo has 

 undergone a great chemical change, and is no longer capable of deve- 

 lopment. The dormant life of the seed must have long ago expired. 

 He concludes that the stories about the germination of these seeds 

 after thousands of years are altogether apocryphal. 



Percival's Agricultural Botany. § — This work is intended to 'aid in 

 the removal of the deplorable ignorance too often displayed by agricul- 

 turists in the first principles of their craft. Its scope will be sufficiently 

 shown by an enumeration of the headings of the chapters : — General 

 External Morphology ; Internal Morphology (Anatomy) ; Physiology of 



* S.B. k. Akad. Wiss. Wien, Oct. 19..1899. See Oesterr. Bot. Zeitschr., I. (1900) 

 p. 25. t Ber. Deutsch. Bot. Ges., xviii. (1900) pp. 122-30. 



t Comptes Rendus, exxx. (1900) pp. 1643-6. 



§ 'Agricultural Botany, Theoretical and Practical,' by John Percival. ^London, 

 Duckworth, 1900, xii. and 798 pp. and 265 figs. 



