108 



BOTANY 



of the metamorphosed members of the plant body described in the 

 preceding chapter ; the resemblance between prickles and thorns, and 

 between haptera and lateral roots will serve 

 as examples. They are not, however, to be 

 traced back in origin to such members (p. 50). 

 Both hairs and emergences frequently 

 act as secreting organs, and are then termed 

 GLANDS. In many cases they are concerned 

 with the active exudation, and at times also 

 the absorption of water. They then belong 

 to the class of organs designated HYDA- 

 THODES ( 104 ) by HABERLANDT. Other glandular 

 hairs excrete 'a resinous substance. The 

 hairs of Primula sinensis (Fig. 117) are in 

 reality such glands, in 

 which the cuticle of the 

 terminal globular head 

 is pressed away from the 

 cell wall by the resinous 

 matter excreted from the 

 hair, until finally the 



Fir.. 110. Glandular colleter bulging CUticle IS ruptured 

 from a stipule of Viola trl- an( j the res inOUS Secretion 

 color, showing also a uni- . . 



cellular hair, (x 240.) exudes. 1 he hairs of this 

 and other species of Pri- 

 mula (especially P. obconica) are capable of excit- 

 ing inflammation in the skin of those handling 

 them ( 10C ). Only some persons are susceptible 

 to the effect. The similar but more complicated 

 glandular hairs of Hops (Fig. 118) produce a 

 secretion called LUPULIN, to which beer owes its 

 bitter taste and distinctive aroma. The secretion 

 is set free by the bursting of the cuticle, the 

 latter having been previously raised up from the 

 underlying cell wall as a continuous membrane 

 (Fig. 118 B}. Hairs and emergences with abund- 

 ant protoplasmic contents occur on irritable 

 stamens, perianth leaves, and pulvini, and, as 

 HABERLANDT ( 105 ) showed, act as tactile papillae, 

 hairs, or bristles in the reception of stimuli. In 

 other cases they are not themselves irritable, but FIG. 120. Digestive gland 

 serve to conduct a stimulus mechanically towards from Drosera rotu " fli - 

 the irritable tissue. 



folia, (x 60.) 



The mucilaginous matter produced in young buds by the mucilage papillae or 

 COLLETERS results from the partial dissolution of the cell wall under the cuticle. 

 After the mucilaginous secretion has been discharged by the ultimate rupture of 



