430 SUMMARY OF CURRENT RESEARCHES RELATING TO 



theory, but concludes that the formation of organs at the apex of a 

 shoot is an extraordinarily complicated process, depending on a whole 

 series of factors, as to whose mode of operation we know next to nothing. 

 No theory of phyllotaxis can be of value which does not take into 

 account the processes which go on within the apex of the growing 

 shoot. 



Variegated Leaves. * — Mdlle. Rodrigue has studied the structure 

 of variegated leaves in 33 species. The white effect is due, in most 

 cases, to the absence of chlorophyll, although a similar appearance is 

 given by certain dissolved pigments, and by the reflection of light. 

 Where chlorophyll is absent, the leaf may be regarded as diseased, and 

 the tissues are different from those of normal leaves, being much thinner, 

 and without any palisade-parenchyme. 



Organs of Exudation, f — J. Goffart calls attention to a prevalent 

 confusion in botanical treatises between the process of secretion and 

 that of exudation (sudation). The former process involves the elimina- 

 tion of viscous, resinous, or other matters not required further for the 

 nutrition of the plant. The latter consists simply in the expulsion of 

 water containing in solution a very small amount of organic and 

 inorganic substances, from 0-007 to 0*12 p.c, chiefly calcium carbonate. 

 The apparatus for the two processes is also entirely different. In his 

 account of the structure of the exudation apparatus, which occurs 

 mostly in the leaves, the author adopts in the main the description of 

 Spanjer.J While secretion requires the aid of a protoplasmic body for 

 elaborating the secreted products, exudation consists simply in filtration 

 through intercellular cavities, the cells which bound these cavities 

 taking only a passive part in the process. The exudating apparatus is 

 in all cases situated at the extremity of a vein, and consists, in its most 

 perfect condition, of vascular bundles, an epithema, the epithemial 

 sheath, and the epithemial epiderm. Exudation takes place in many 

 aquatic plants ; then through pores at the apex of the leaves. 



Roots of Herbaceous Plants. § — T. Freidenfelt classifies the roots 

 of herbaceous annuals under the following heads: — (1) Ruderal type 

 (Galeopsis, Lamium, Myosotis, Veronica, Viola, &c.) ; the primary root 

 soon branches ; adapted for energetic absorption ; (2) Tap-root type , 

 adapted for fixing the plant firmly in a dry or sandy soil ; (3) Central 

 type, intermediate between these two (Lapsana, Atriplex, Draba). In 

 saprophytes and in annuals provided with haustoria (root-type of hemi- 

 parasites), the root-system is greatly reduced, and the development of 

 lateral roots but feeble. 



Tuberous Rootlets of Cycas. || — A. C. Life has studied the coral- 

 like outgrowths from the ascending rootlets of roots of Cycas revoluta. 

 The tubercles contain a central vascular cylinder and a very thick cortex, 

 about midway in which is a zone coloured green by an endophytic alga. 

 They are abundantly supplied with lenticels, and their primary func- 



* Mem. Herb. Boissier, xvii. (1900). See Bot. Gazette, xxxi. (1901) p. 209. Cf. 

 this Journal, ante, p. 296. t Bull. Soc. R. Bot. Belgique, 1900, pp. 54-80. 



t Cf. this Journal, 1898. p. 554. 



§ Bot. Not., 1900, Heft 5, 15 pp. See Bot. Centralbl., lxxxvi. (1901) p. 156. 

 || Bot. Gazette, xxxi. (1901) pp. 265-71 (10 rigs.). 



