Chapter X — 117 — Drosera 



Some species, after the seedling stage is passed, form tubers which 

 perennate, and send up strong stems ending in a rosette or whatever 

 type of above-ground parts it has. From the stems grow axillary, 

 positively geotropic shoots (droppers), at the ends of which new tubers 

 arise {See beyond for details). These species have no roots, while in 

 general the roots are always meagre in numbers and extent, a fact 

 which is well known (Schmid). The root hairs are numerous in some 

 species and their walls are suberized and persistent. In other species 

 the root hairs are sparse. Marloth has reported both conditions in 

 S. African species. In some species the roots are apparently replaced 

 by rhizoids. Diels has thus described for D. erythrorhiza the root-like 

 productions one to three in number from the base of each scale leaf. 

 These have no root cap, but are provided with "root" hairs (Diels 

 1906). GoEBEL comments on the nature of these structures, called 

 by the equivocal name of leaf-roots ("Blattwurzeln"), pointing out 

 that in the apex, while no root cap is present, there is an apical mer- 

 istem just behind the epidermis, the outer walls of which are thick- 

 ened, and which are evidently a protective mail for a boring apex, 

 which may be regarded perhaps as a reducing or reduced root end. 

 Their origin according to Diels, however, is exogenous, and he called 

 them leaf rhizoids, but leaves details of their origin not fully under- 

 stood. I have verified Diels' observation. 



I have examined the "leaf roots" of D. erythrorhiza from West 

 Australia and am able to confirm Goebel's observation of very thick 

 outer cell walls of the apical cells (75 — 19). There is a meristem, but 

 this does not lie immediately behind the epidermis, but just back of 

 three cell layers within. The apex itself is composed of enlarged 

 epidermal cells underlain by other cells of similar appearance derived 

 from two subepidermal layers, and heavily loaded with large starch 

 grains. The apical cells constitute a boring organ which does not 

 slough off as does the root cap. If there is any renewal of substance, 

 this would be in new secretion of cell wall. The plant grows, however, 

 in very loose soil where friction against the growing tip is minimum in 

 amount. At all events I have examined a large number of "leaf- 

 roots" and have not found any evidence of renewal of epidermal cells. 



In the axis of each rhizoid-bearing scale small tubers, having evi- 

 dently the function of reproduction, can be produced (Goebel 1933). 



Unfolding movements of the leaf. — In many of the species of Dro- 

 sera {D. rotundifolia, D. pygmaea), the petiole is bent so that the 

 upper face of the blade becomes applied to the petiole {16 — 17). This 

 is brought about by the hyponasty of a more or less narrow zone of the 

 petiole at the base of the blade. In other species, however, 

 those in which the leaf blade is slender and filiform, there oc- 

 curs true circination, as in D. filiformis, D. regia (with slender 

 ligulate leaves with short petioles), D. binata, D. dichotoma, with 

 the volute facing the stem, and due again to hyponasty. Just 

 the opposite occurs in Drosophyllum and in Byblis linifolia. These 

 two directly opposite behaviors appear, according to Fenner (1904), 

 to be related to the need for protection of the tentacles since they are 

 on the upper surface in Drosera and on the lower in Drosophyllum, 

 but, it is to be noted, along the margins in both, with the result that 



