510 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



tetrapolar, and the rootlets arise normally and are arranged in four rows. 

 Their growth is limited, and they do not branch ; they are very slender, 

 measuring scarcely ' 8 mm. in diameter. While these rootlets show a 

 normal cortical structure, they are remarkable in having an extremely 

 simple stele. It is limited by an evident bundle-sheath and has a 

 regular pericambium, but the wood consists only of a single tracheid in 

 contact with the rhizogenous layer ; the rest of the bundle consists of 

 3 to 10 uniform phloem elements with thin walls. The bundle is thus 

 unipolar, and the rootlet has a bilateral symmetry, the plane of which 

 passes through the axis of the main root. 



This is the only known example of a root of a seed-plant with a 

 unipolar bundle. This reopens the question of the morphology of the 

 abnormal roots of Isoetes and certain Lycopods, which have been 

 regarded as half -roots or as roots with a bent bipolar bundle. Similarly 

 the rhizophores of Selaginella and the appendices of Stigmaria may be 

 analogous cases of reduction of the phloem and xylem of a root. 



Anatomy of certain Groups of Caryophyllacese.* — F. Joesting has 

 studied the anatomical structure of the vegetative .organs of a number 

 of genera of the following sections of this order : — Spergulea?, Polycarpeae, 

 Dysphanieee, SclerantheEe, and Pteranthese. He draws attention to the 

 extraordinarily primitive leaf-structure of the majority of the plants of 

 these groups ; a differentiation into palisade- and spongy-parenchyma is 

 shown only in the arrangement, rarely also in the form of the cells. 

 Another very general character is the segmentation of the wood-cylinder 

 by wedges and parenchymatous tissue, especially in the root, but also 

 the stems which show a well-marked growth in thickness. He also 

 notes the segmentation of the whole root by obliteration of the central 

 tissue ; this leads in an extreme case {Telephium Imperati) to a complete 

 breaking up' of the root into five " branches," each of which shows a 

 centric structure and a cork-envelope. The roots of species of Spergularia, 

 Spergula, Telephium, Polgcarpcea, and others show a remarkable secondary 

 formation by means of extrafascicular secondary cambiums. 



Petiolar Glands of Viburnum Opulus.f — M.kThouvenin describes 

 the histology and the relation to the vascular bundle system of the 

 petiole of the small gland-like stipules and the petiolar glands of this 

 species. He discusses the morphology of these structures and suggests 

 that they may represent reduced lateral leaflets of a compound leaf ; 

 these leaflets, the anatomy indicates, were sessile and inserted on the 

 rhachis by a broad base. 



Modification of Habit by Grafting.^ — L. Daniel, continuing his 

 investigations on this subject, records the following conclusions. In 

 the case of Composites the grafting of annual parts of herbaceous plants 

 on appropriate herbaceous stocks may modify the period of duration and 

 prolong the flowering season of the graft. The grafting of an herbaceous 

 plant on an annual plant may prolong the life of the latter. Thus 

 Solatium pubigerum was grafted on the giant tobacco, an annual in the 



* Beih. Bot. Centralbl. (Original-Arbeit) xii. (1902) pp. 139-80 (2 pis.), 

 t Kev. Gen. Bot., xv. (1903) pp. 97-103 (6 figs, in text). 

 X Comptes Kendus, cxxxvi. (1903) pp. 1157-9. 



