196 SUMMARY OF CURRENT RESEARCHES RELATING TO 



lamella retain their protoplasmic character. The vexed question as to 

 the origin of callus is discussed, and reasons are given for the view, pre- 

 viously suggested by Rendle in the case of the callus-formation in the 

 " vesicular vessels " of the onion, namely, that it may be formed partly 

 by alteration of the cell-wall, partly by deposition from the protoplasm. 

 The function of the callus rods seems to be the regulation of the size 

 of the pores of the active sieve-plate, while the further development of 

 the callus-cushions finally closes them entirely. 



Structure of the Tuberous Boots of Thrincia tuberosa.* — A. Maicre 

 and C. L. Gatin find an interesting and peculiar method of secon- 

 dary thickening in the roots of this Composite which is common in 

 the neighbourhood of Algiers. At the base of the stem each year 

 are formed adventitious roots which become much thickened noar 

 their point of insertion. The primary structure is normal, but whereas 

 in the non-tuberous upper part of the root a normal cambium layer 

 is produced, in the tuberous portions this is replaced by a number 

 of separate layers. Each of these surrounds a bundle of primary wood, 

 and produces on the outside secondary parenchyma in which are formed 

 islands of secreting cells, and on the inside radiating threads of poly- 

 hedral cells, some of which become differentiated into wood-vessels. 

 There are thus formed at the periphery of the central cylinder a number 

 of rounded areas of secondary tissue, each resembling a small stele. 

 The cortical layers become stretched and divided tangentially to allow 

 of this increase in bulk of the central tissues. Inulin is secreted in 

 these secondary formations, and subsequently used by the plant as it is 

 not found in the withered tubers. 



Sucker of Loranthus aphyllus.f — Sir W. T. Thiselton-Dyer de- 

 scribes the external appearance of the haustorium of this remarkable 

 leafless parasite which grows on the leafless spine-bearing stems of the 

 Chilian Cereus Quisco. The sucker has a thalloid appearance and 

 ramifies widely in the cortex of the host, sending up aerial shoots which 

 always emerge on the upper side of the spine-tufts. An examination of 

 the anatomy of the structure by Mr. L. A. Boodle showed that the 

 sucker is completely covered by a layer of periderm formed in the 

 enveloping cortex of the cactus. 



Bladders of Utricular ia.— H. Meierhofer | has studied the develop- 

 ment of the bladders in several species of Utricularia, and has estab- 

 lished that, from a morphological point of view, they are leaves or 

 segments of leaves. Though they unquestionably act as floating organs, 

 they are not indispensable to the plant in this respect. While the 

 " antennae " prevent the access to the bladders of animals of any con- 

 siderable size, he attributes importance to the fact that the ciliated 

 Infusorians, especially Paramsecium caudatum, are positively chemo- 

 tactic to weak acid solutions. All the shoots, even the smallest (in 

 U. vulgaris) form winter-buds, and the production of ripe speeds is rare. 

 All the glands, both the 2-armed and the 4-armed, are trichomic, 

 originating from a single epidermal cell. The nutritive or insectivorous 

 function of the bladders was fully established. 



* Comptes Rendus, cxxxiv. (1902) pp. 302-3. 

 t Ann. Bot, xv. (1901) pp. 749-57 (1 pi.). 

 X Flora, xc. (1902) pp. 84-113 (9 pis.). 



