08 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of roots and shoots is due to external conditions. Roots of dandelion, 

 which under uniform conditions of moisture, form roots at the lower 

 and shoots at the upper end, gave an opposite result when the upper 

 <md was placed in water the lower end projecting into the air ; shoots 

 then developed on the exposed end and none on that in the water. When 

 cuttings of the stems of Ribes aureum were placed with their basal ends 

 in water and their apical ends in moist air, roots were formed only on 

 their apical ends. Similar results were obtained with Salix vitellina, 

 showing a marked tendency for the roots to appear only where there is 

 a sufficient supply of air. When cuttings were rotated horizontally, 

 the centrifugal force acted as a check on development, the inhibition 

 being in proportion to the force ; thus, if the apical end describe the 

 greater circle, the buds there are inhibited more than those at the 

 opposite end. In this way the usual polarity may be reversed. 



Animal Parasites and Floral Teratology.* — Marin Molliard con- 

 siders that the virescence of the flower which is frequently met with in 

 TrifoUum repens is due to the presence of the larva of a Ritgnophora 

 (probably Hylastinus obscurus) which lives in the stem of the plant, in 

 which it bores a long gallery. He found this larva in fifty virescent 

 specimens collected in two localities near Paris, whereas it was absent 

 from normal plants growing near. Similarly virescent individuals of 

 TrifoUum pratense contained the same insect. The larva forms the 

 galleries especially in the pith, whence it penetrates between the vascular 

 bundles to reach the cortical tissue. One result is that many of the 

 wood-vessels become clogged by a gummy substance, which will ob- 

 viously interfere with the circulation of the sap. Similar facts have 

 been noted in other plants. Thus, in a specimen of Melilotus arvensis 

 with strikingly virescent flowers, the author found a larva of one of 

 the Curculionidas, while neighbouring normal individuals showed no 

 trace of the insect. The author suggests that the abnormal develop- 

 ment of the flower is a traumatic action, resulting from a profound 

 modification of the conditions of nutrition caused by the mining opera- 

 tions of the insect, which acts at some distance from the flower. 



Colour Changes ' in Fungi and Bacteria.f — T. Milburn has 

 experimented with Hypocrea rufa, H. gelatinosa, Aspergillus niger, and 

 Bacillus ruber-balticus. He tested the influence of culture media, 

 osmotic pressure, light, temperature, etc., on the development of the 

 pigments. He finds that with increasing osmotic pressure pigment- 

 formation in the conidia of Hypocrea rufa is white, and that conidial 

 formation is retarded : that acid media induce the formation of green 

 conidia ; while in alkaline media yellow conidia are formed. Well 

 nourished mycelium fails to produce conidia, while a supply of oxygen 

 or lowered nutrition induces conidial formation. Aspergillus niger 

 forms a yellow as well as a black pigment. It is sensitive to light, and 

 from yellow becomes grey or black. Bacillus ruber-balticus is influenced 

 by the nature of the culture media to produce violet or orange 

 •colorations. 



* Comptes Rendus, cxxxix. (1904) pp. 930-2. 



t Centralbl. Bakt., xiii. (1904) pp. 129-38; 257-76 (2 pis. and G figs.). 



