PART I. MORPHOLOGY. 



[14 



to branch. On roots, at any rate, they are developed in acropetal 



succession. 



(6) Emergences. These appendages differ from hairs in that 



they are developed not only from superficial cells, but from others 

 lying beneath them. 



The commoner forms of emergences are prickles, 

 (Fig. 32) and warts ; more specialised forms are 

 the tentacles of the leaf of Drosera (Figs. 33 and 

 34) ; the ligule of the leaf of Grasses (Fig. 19 A), 

 Selaginella, and Isoetes ; and the corona of Nar- 

 cissus. 



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 Algae (e.g. Laminaria), on the 



stems and branches of Podostemacese and on 



the tendrils of some Ampelidese and Bigno- 



niaceae among Phanerogams : it contains no 



vascular tissue even in Vascular Plants. 

 The suckers, or haustoria, of parasitic 



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



Rhinanthus, etc.), are also emergences, being 



FIG. 32. Prickles 

 on the stem of the 

 Rose (nat. size). 



Fio. 33.-Leaf of Drotera rotundifoha. A Expanded ; d the 

 mdular tentacles of the edge of the leaf ; m the short ten- 

 tacles in the middle. B The marginal tentacles have bent 

 towards the middle at the touch of an insect, x. 



FIG. 34. Tentacle of 

 Drosera rotundifolia. (Af- 

 ter Strasburger : x 60.) 



