610 SUMMAEY OF CUERENT RESEARCHES RELATING TO 



the cells of the layer from whicli they are produced become punctated 

 with thick cell-walls like certain cells of the cortex, while large quantities 

 of starch are formed in their interior, Dr. G. Haberlandt comes to the 

 conclusion that the initial cells of the medullary rays acquire during the 

 winter new functions connected with the transport of sap, and resembling 

 those of the cortex. 



(5) Structure of Organs. 



Adventitious Roots.* — Sig. N. Terracciano found in a hollow in the 

 trunk of a Cupressus sempervirens, two sets of adventitious roots, one above 

 and one below, both variously ramified and independent of one another. 

 After citing other similar cases, the author explains the adventitious pro- 

 duction and the ascending course of the roots, by supposing that the lower 

 roots which originated from the cambium layer of the trunk becoming 

 inserted in the hollow, and the upper roots from the cambium layer of the 

 branch descending into the cavity, and that they took their ascending course 

 from compulsion, assisted by the damp mould in the cavity. 



Tubercles on the Roots of Leguminosse-t — From a very exhaustive 

 examination of these structures, Herr A. Tschirch states that he has never 

 found them wanting in any species of LeguminosEe examined, whether 

 annual or perennial ; they occur only on the underground organs, and 

 always on the roots, never on underground stems. They are of two kinds, 

 the lupin type and the robinia type. 



The first type belongs almost exclusively to the genus Lupinus, and is 

 found especially at the crown of the root. The tubercles are here swell- 

 ings of the central vascular bundle of the root itself, having the appearance 

 of an ordinary hypertrophy, and extending afterwards to other portions of 

 the tissue, and forming a tuberous swelling. In the second and more 

 generally distributed type, the origin of the swelling is always lateral ; its 

 mature form varies greatly. The two types vary also widely in their 

 mode of development. In Lupinus, the centre of the swelling is occupied 

 by a semicircular or roundish mass of tissue, which Tschirch calls the 

 hacteroid tissue (the bacteria of Woronin, bacteroids of Brunchorst), almost 

 always capable of growth. The entire tubercle is surrounded by an 

 envelope of cork ; root-hairs are always wanting. Starch is found in this 

 tissue, especially in its early stages. By the time that the seeds are ripe, 

 this tissue has become entirely emptied of its contents, and the tubercle 

 dies away. In Bohinia, Phaseolus, &c., on the contrary, the bacteroid 

 tissue occurs at the apex of the tubercle, and continues to grow as its lower 

 part becomes emptied of its contents. 



The author agrees with Brunchorst that the so-called " bacteroids " are 

 not living parasitic organisms, but organized albuminoid structures ; the 

 chief arguments for this view being their variable form, the invariable 

 failure of all attempts at culture, and their behaviour towards staining 

 reagents. They appear to approach most nearly in their properties to the 

 group of caseins ; and the tubercle must be regarded as a transitory store- 

 house of albuminoid reserve-material, to be used as wanted by the plant, 

 especially in the maturing of the seeds. 



With regard to the filiform structures which commonly (but not in- 

 variably) accompany the bacteroid tissue, and which have been regarded 

 by previous observers as the hyphse of parasitic fungi, or as plasmodial 



* Eend. R. Accad. Sci. Fis. e Mat. Napoli, 1886, 1 pi. 



t Bur. Deutsch. Bot. GeselL, v. (1887) pp. 58-98 (1 pi.). Cf. this Journal, 1886, 

 p. 271. 



