780 SUMMARY OF CURRENT RESEARCHES RELATING TO 



reasons for regarding the petals and sepals, not as modified entire leaves, 

 but as modifications of the base of the petiole or stipule, the main 

 purpose of both organs being the protection of the tender parts of the 

 flower. It is not uncommon in the rose for the ordinarily suppressed 

 lamina of the leaf to reappear, in cultivation, at the apex of the sepals. 



Stem and Leaf of Utricularia.* — According to Prof. K. Goebel 

 several exotic species of Utricularia exhibit a remarkable absence of 

 differentiation between axial and appecdicular organs. We have here 

 leaves which have the power of developing into organs, the stolons, which 

 have all the characters of a shoot; while, on the other hand, in some 

 species, large cylindrical bladder-bearing stolons become flattened off at 

 their ajiices into leaves. 



Opening and Closing" of Stomates.t — Prof. S. H. Yines assigns 

 reasons for his conclusion, derived from observation of the jDhenomena 

 connected with the opening and closing of stomates, that the opening is 

 not due to stimulation by light or any other agent of the irritable 

 protoplasm of the guard-cells, but is a purely passive one, depending on 

 the formation of osmotically active organic substances in the chloro- 

 phyllaceous guard-cells when exposed to light; while, on the other 

 hand, their closing is an active process determined by the stimulating 

 influence of a certain relation between loss and supply of water on the 

 irritable protoplasm of the guard-cells. 



CoUeters and Glands of Gunnera.J — Herr P. Merker describes the 

 colleters on the leaves of various species of Gunnera as being formed 

 originally of three epidermal cells, other parenchymatous cells immedi- 

 ately beneath the epiderm subsequently taking part in their formation, 

 and forming their foot. The mucilage in the glands of the stem is 

 the seat of the peculiar colonies of Nostoc so often found in several 

 species. The author does not regard these as carrying on a symbiotic 

 existence, but rather as parasitic, and inflicting injury on the host. 



Abnormal Formation of Eliizome.§ — Herr H. Vochting describes 

 the production of rhizomes on aerial stems of Stacliys tuberifera and 

 S. palustris. These resembled the normal rhizomes in all essential 

 particulars, differing chiefly in the greater length of the internodes, in 

 the scales laeing replaced by leaves, and in the presence of chlorophyll. 

 They serve to show the close morphological connection between under- 

 ground and aerial stems. 



Aerating Roots.|l — Prof. W. P. Wilson describes the mode of growth 

 in the excrescences known as " knees " which characterize the American 

 cypress, Taxodium distichum, when growing in swamps. He finds that 

 they are undoubtedly for the purpose of aerating the plant ; and that it 

 is quite possible to produce similar aerating organs in other plants by 

 growing them in very swampy localities. 



* Flora, Ixxii. (1889) pp. 291-7 (I pi.)- Cf. this Journal, ante, p. 545. 



t Ami. of Bot., ill. (1889) pp. 271-4. % Flora, Ixxii. (1889) pp. 211-32 (3 pis.). 



§ Bot. Ztg., xlvii. (1K89) pp. 501-7 (1 pi.). 



II Proc. AcarL Nat. Sci. Fhilad., 1889, pp. 67-9. 



