66 



PART I. THE MORPHOLOGY OB' PLANTS. 



[14. 



or even on leaves (e.g. Salvinia). They are always unicellular, and it is 

 only rarely that they are found to branch. On roots, at any rate, they are 

 developed in acropetal succession. 



(b) Emergences. These appendages differ from 

 hairs in that they are developed not only from super- 

 ficial cells, but from others lying beneath them. 



The commoner forms of emergences are pricJdes 

 (Fig. 41) and warts ; more specialised forms are 

 the tentacles of the leaf of Drosera (Figs. 42 and 

 43) ; the ligule of the leaf of Grasses (Fig. 28), 

 Selaginella, and Isoetes (see p. 48) ; the corona of 

 Narcissus ; the cupule of Lunnlaria and Marchantia. 

 The more highly developed emergences (e.g. many 

 prickles, tentacles of Drosera) of Vascular Plants 

 frequently contain vascular tissue. 

 A remarkable kind of emergence is the organ 

 of attachment, termed a hapteron, developed on 

 the stalks of some Algee (e.g. Laminaria), on the 

 stems and branches of Podostemaceae and on the 

 tendrils of some Ampelidese and Bignoniacese 

 among Phanerogams : it contains no vascular 

 tissue even in Vascular Plants. 



The suckers, or haustnria, of parasitic plants, 

 (e.g. Cuscuta, Orobanche, Thesium, Rhinanthus, 

 etc.) are also emergences, being developed from 

 the cortical tissue of the root or stem bearing 



FIG. 41. 

 Prickles on the 

 stem of the 



Rose (nat. size). 



FIG. 42. Leaf of Drosera rotundifolia. A Expanded ; d the 

 glandular tentacles of the edge of the leaf ; m the short tentacles 

 in the middle. B The marginal tentacles have bent towards 

 the middle at the touch of an insect, x. 



FIG. 43. Tentacle 

 of Drosera rotundifolia. 

 (After Strasburger: x 



