612 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the helicoid portions, and in those which are in close contact with the 

 support; in the former case motility, in the latter case rigidity of the 

 coils is the controlling factor, and the anatomical structure of the two 

 regions therefore varies more or less. The two regions agree in the fact 

 that their most important requirements are in connection with unilateral 

 functions, and hence in the structure being dorsiventral. This dorsiventral 

 structure is usually visibly indicated externally in both regions by a 

 broadening on the concave side on a transverse section, commencing either 

 with the origin of the organ, or more often at a later period. 



Pitchers of Sarracenia.* — Herr P. Zipperer finds in Sarracenia 

 purpurea, as in other species of the genus, that the pitcher secretes a fluid 

 containing a diastatic and peptonic ferment, by which insects are killed, 

 and the whole of their soft parts assimilated. 



Formation of Hairs.f — Herr F. Krasan discusses the cause of the 

 woolliness of the galls so commonly produced on several species of Thymus 

 by the attacks of a Phytoptus. The hairs which cover these galls are in 

 no way different from the normal trichomes of the plant, and especially 

 from those which cause the woolliness of the variety T. Chamsedrys var. 

 lanuginosa, which frequently grows intermixed with individuals of the 

 glabrous form attacked by the parasite, especially in very sunny situations, 

 or where there are great and rapid alternations of heat and cold. 



With these galls on Thymus may be compared the morbid structures 

 known as phyllerium or erineum, tufts of hairs on the lamina of the leaf, 

 very common on the vine, alder, lime, and on many herbaceous plants. 

 Though these are generally believed to be caused by the attacks of mites, 

 it is exceedingly difficult to detect the parasite in connection with them, 

 and the disease is especially prevalent after injury by late frosts, followed 

 by a period of intensely hot weather. The author believes that the forma- 

 tion of hairs does not result in these cases from the attacks of the parasite, 

 but that both phenomena are due to the same cause, viz. special vital con- 

 ditions, and especially the irritation caused by sudden and unusual changes 

 in these conditions. The most prolific cause of irritation is an over- 

 saturation of the organisms with ammoniacal substances and phosphorus 

 salts, and consequent degeneration of the sap. This tendency is materially 

 increased in the case of galls by the irritation resulting from the injury 

 inflicted on the tissues by the parasite. 



Iformal Position of Zygomorphic Flowers. f — Dr. F. Noll continues 

 his researches on this subject, his latest observations being chiefly on the 

 obliquely and transversely zygomorphic flowers of the Solanaceae and 

 Fumariacese, those of inverse origin of the Orchidese, Lobeliaceae, and 

 Balsaminese, and on leaves. The mathematical side of the subject is largely 

 illustrated by formulse. In addition to the ordinary and well-known 

 changes in direction, the phenomena of torsion involve here, in many cases, 

 a new kind of movement, exotropic lateral motion. It is this movement 

 which causes the external position of the organ on its mother-axis, and 

 hence its development in relation to the parent-plant. External forces do 

 not play any direct part in bringing this about; the development is in- 

 fluenced by the mother-plant itself. The assumption of this exotropic 

 motion, which can be experimentally confirmed, explains, in the simplest 



* Zipperer, P., Beitr, z. Kenntniss d. Sariaceniaceen. Erlangen, 1886, 34 pp. and 

 1 pi. See Bot. Centralbl., xxis. (1887) p. 358. 



t Oesterr. Bot. Zeitschr., xxxvii. (18S7) pp. 7-12, 47-52, 93-7. 



j Arbeit. Bot. Inst. Wiiiv.burg, iii. (1887) pp. 315-71 (8 figs.). Cf. this Journal, anie, 

 11. 2tj6. 



