PHYSIOLOGY. 



277 



Fig. 247 represents several forms of these organs. First, 

 sessile, a, in the form of papillae, as found on each side of the 



Fig. 247. 



mid-rib of the leaves of the Passion Flower, (Passiflora 

 lunata.) Also sessile, b, in the form of a papillary gland 

 covering detached scales, as in the Rhododendron puncta- 

 tum. 



Second, pedunculated. This exhibits various forms. Thus 

 on the foot-stalk of the leaf of the Nectarine (Amygdalus 

 Persicus,} it resembles a shallow cup, c, supported by a pedi- 

 cel or stand, from the cavity of which exudes the secretion. 

 This part is not covered by the epidermis. In the Castor Oil 

 plant (Ricinis communis,) it resembles a small round nail d, 

 and in this also the exuding surface is naked of the epider- 

 mis. In the upper surface and around the edges of Sundew 

 leaves, the glands are cup-shaped, and supported by a short 

 foot-stalk e. On the Moss Rose, the stems and buds of which 

 are covered with these organs, giving them a moss-like ap- 

 pearance, they are branched, as seen at , which, like the 

 others, is a magnified representation. 



ABSORPTION OF NUTRIMENT BY PLANTS. 



The greater number of cellular plants absorb water with 

 nearly equal facility from every part of their surface : this is 

 the case with the Alga, for instance, which are aquatic plants. 

 In Lichens, on the other hand, absorption takes place more 

 partially ; but the particular parts of the surface where it oc 

 curs are not constantly the same, and appear to be determined 

 more by mechanical causes than by any peculiarity of struc- 

 ture some, however, are found to be provided in certain 

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