250 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Both they and the thicker roots are but sparsely endowed with root- 

 hairs. When these slender roots come into contact with organic 

 substances in tho substratum, protuberances are formed on them, the 

 structure and mode of formation of which are described in detail. In 

 some cases both the nutrient object and the protuberance are invested 

 by a number of fine hairs sjiringing from the latter. From its apex the 

 protuberance puts out a kind of clasp by which it attaches itself to the 

 nutrient object, somewhat after the manner of a haustorium, some of the 

 cells of the protuberance actually penetrating into the nutrient substance. 

 These protuberances have often only a temporary existence, perishing 

 with the complete decay of the nutrient substance. 



The special function of these organs the author believes to be the 

 absorption from the soil of nitrogenous food-material. 



Haustoria of the Rhinantheae and Santalacese.* — M. Leclerc du 

 Sablon states that whilo non-parasitic phanerogamous plants absorb the 

 necessary liquid food by means of the root-hairs, parasites, such as 

 Cuscuta and Orobanche, absorb liquids by means of special organs called 

 haustoria (siuyoirs). In a third category of phanerogamous plants the 

 modo of nutrition partakes somewhat of the above two methods combined. 

 In the Rhinantheae and Santalaceae the absorption of liquids takes place 

 both by root-hairs and by haustoria. 



The author describes the haustoria of the Rhinantheae, taking Melam- 

 pyrum pratense as an example. The roots of this plant are normally 

 destitute of root-hairs ; the haustoria commence to form towards the 

 extremity of the roots shortly after germination. A slight projection is 

 seen on the sides of the root ; the two layers of cells which constitute 

 the cortical parenchyma elongate radially, and divide by septa in 

 different directions. This is the commencement of the formation of 

 the haustorium. In the Santalaceae the commencement of the formation 

 of the haustorium is first seen in a layer of cells beneath the superficial 

 cells of the cortex of the root, the superficial cells being already dead. 



In another paper by the same author,f the development and structure 

 of haustoria in lihinantheae and Santalaceae are more minutely described. 

 In the Rhinantheae both cortex and pericycle take part in the formation 

 of haustoria. On the sides of the haustoria the cells of the piliferous 

 layer develope into root-hairs ; towards tho extremity a certain number 

 of cells become differentiated, and penetrate into the host. The absorb- 

 ing cells advance into the tissue of the host, either in a bundle or more 

 often isolated. The Rhinantheae, then, in every case absorb their 

 liquid nutriment by means of the cells of the piliferous layer. In the 

 Santalaceae, and especially in Osyris, which bears few haustoria, root- 

 hairs are formed. In this family the haustoria are also formed by the 

 cortex and pericycle, but here the pericycle plays a more important part 

 than in the Rhinantheae. In the portion of the haustorium near to the 

 root, a central cylinder and a cortex can be distinguished ; the limit is 

 marked by an endoderm. Towards the extremity of the haustorium the 

 endoderm disappears, and at the same time the distinction between cor- 

 tex and central cylinder. 



In every case the absorbing cells are connected with the xylem- 

 bundles of the root by a bundle composed of spiral cells. 



* Comptes Bendus, cv. (1887) pp. 1078-81. Cf. this Journal, ante, p. 80. 

 t Ann. Sci. Nat., vi. (1887) pp. 90-117. 



