588 SUMMARY OF CURRENT RESEARCHES RELATING TO 



connected with the dispersion of the rays of light in the dense pali- 

 sade-tissue. They always have their principal axis vertical to the 

 surface of the leaf, and are fixed in this position by a peculiar band of 

 cellulose. The rays of light fall, therefore, parallel to the principal 

 axis of the crystals, and are dispersed on all sides from their reflect- 

 ing surfaces, while those which pass through the crystals are refracted 

 obliquely. It is possible that the subepidermal cystoliths in the 

 leaves of Ficus have a similar property. 



Swellings in the Roots of Papilionacese.* — ¥. Schindler has 

 reinvestigated this subject, with reference to the previous researches 

 of other observers ; and has come to the conclusion that the peculiar 

 swellings are not due to the attacks of a parasitic fungus, but to 

 hypertrophy of the tissue surrounding the vascular bundles, though 

 in some cases there appears to be a phenomenon akin to symbiosis. 

 The species in which the peculiar structures were observed, were 

 Trifolium pratense, Vicia villosa, Phaseolus vulgaris, and Lupinus. 



Origin of Adventitious Roots in Dicotyledons.t — A. Lemaire 

 discusses Van Tieghem's statement that lateral roots have their origin 

 in the peripheral layer of the central cylinder which he denominates 

 the pericycle, and points out that all Van Tieghem's examples are 

 drawn from Monocotyledons. Lemaire finds among Dicotyledons two 

 types, the first in which they spring from interfascicular spaces, the 

 second from the pericycle, or layer of the central cylinder immediately 

 beneath the endoderm. In the latter case they are always produced 

 in the neighbourhood of large primary bundles. The cellular portion 

 of the pericycle of two plants examined (Mentha arvensis and Veronica 

 Beccahunga) divides by tangential walls into two layers, the inner of 

 which produces the central cylinder, the outer one again dividing into 

 two layers. The lower of these gives rise to the cortex, while the 

 peripheral layer developes, by successive divisions, into the cap and 

 piliferous layer of the root. 



Crystals of Silex in the Vascular Bundles.! — Pursuing the 

 researches of G. Licopoli, E. F. SoUa has examined the clusters of 

 siliceous crystals found in the fibrovascular bundles of a number of 

 species of palm, especially Chamcerops humilis and Phoenix dactylifera. 

 He finds them in rows in the immature fruit of the first-named and 

 in the trunk of the last-named species, in the latter case occurring 

 also in the vascular sheath. They are found also in the scleren- 

 chymatous cells in the endosperm of the seeds of Chamcerops humilis, 

 and in the spathe of Cocos Yatai, They vary greatly in size according to 

 the species ; their chemical reactions show them to consist of pure silica. 



Effect of Heat on the Growth of Plants. § — Following out his 

 researches on this subject, J. Wortmann gives the minimum, the 

 optimum, and the maximum temperature for growth in various plants. 

 As a general law, it may be stated that thermotropism is a phe- 



* Bot. Centralbl., xviii. (1884) pp. 84-9. Of. this Journal, iii. (1880) p. 115. 



t Bull. Soc. Bot. France, xsx. (1884) pp. 283-5. 



X Nuov. Giorn. Bot. Ital., xvi. (1884) pp. 50-1. 



§ Biol. Centralbl., iv. (1884) pp. 65-71. Cf. this Journal, iii. (1883) p. 873, 



