108 DERMAL SYSTEM 



It was found that leaves from which the wax had been carefully wiped 

 off transpired 4'03 grams of water per sq. dcm. in a day; control 

 specimens with their waxy covering intact lost 3 '6 grams under the 

 same conditions. A second experiment gave as corresponding values 

 4 - 63 grams and 3 "03 grams. The leaves thus lost on an average 

 30 per cent, more water when the wax was removed. Tschirch has 

 obtained very similar results with the leaves of Eucalyptus globulus. 

 These experimental data accord with the fact that waxy coverings are 

 especially prevalent among xerophytes, such as the Mediterranean 

 species of Dianthus and Euphorbia, the Australian Acacias and 

 Myrtaceae and numerous steppe- and desert-plants (e.g. Capparis 

 spinosa, various Cruciferae and Kubiaceae, etc.) Tittmann has 

 shown that certain spp. of Sedum and Echeveria produce less wax 

 if transpiration is artificially diminished by growing the plants in a 

 damp atmosphere. Waxy coverings may influence the transpiratory 

 activity of the plant in a different way by preventing its surface from 

 being wetted by drops of rain or dew ; the capillary occlusion of 

 stomata is often avoided in this way. In certain cases (Euphorbia 

 Tirucalli, spp. of Strclitzia) each stoma is surrounded by a ring of wax, 

 which thus forms an external air-chamber (cf. Chap. IX.). 



According to the observations of Kerner and Delpino, a waxy 

 covering or bloom sometimes (Salix daphnoides and S. pruinosa, 

 Fritillaria imperialis, various Umbelliferae, etc.) serves to create a 

 slippery surface, and thus to prevent the access of ants to floral 

 nectaries. The author has himself watched the behaviour of small 

 ants which he transferred from the extrafloral nectaries of Vicia 

 sepium to the bloom-covered scape of Hyacinthus sylvestris ; on the 

 treacherous waxed surface the insects moved very slowly, and only 

 by dint of much exertion and at the cost of many slips, whereas 

 a zone, several centimetres in width, from which the wax had been 

 removed, was traversed with the greatest ease. Waxy coverings 

 may thus secondarily acquire an ecological significance in connection 

 with the relations between plants and animals ; this statement in all 

 probability applies more especially to stems in which the wax is 

 confined to or at any rate is more strongly developed on certain 

 comparatively circumscribed areas (e.g. the nodes in the Sugar-cane 

 and in certain Bamboos). 



Since wax, in the form of granules or rods, is easily rubbed off, it 

 is an advantage if the plant is able to regenerate a waxy coating that 

 has been removed. As a matter of fact, a considerable number of 

 plants do possess this capacity ; in the case of Rubus bifiorus and 

 Macleya cordata the act of regeneration may even according to 

 Tittmann be repeated several times in succession. 



