THE NECTAR GLAND IN CACTI 151 



of Gymnosporangium. 6 If, however, a median longitudinal sec- 

 tion of a gland, with the epidermal membrane attached at both 

 extremities, is similarly treated, it is seen that it lengthens and, 

 in consequence, forms a deeper arch. One measurement showed 

 that a membrane which was 10.5 units in length in water, lengthened 

 when dehydrated to 11.6 units, an increase in length of 9 per cent. 



Without attempting an explanation of this peculiar behavior, 

 it is pertinent to observe that, supposing the drying out of the 

 epidermis to cause expansion of the cuticle, one might invoke 

 this to explain the tearing away of the cuticle from the epi- 

 dermal cells. That such an enlargement does occur is a mat- 

 ter of observation, but results, not in consequence of the accu- 

 mulation of secretion, but rather upon exposure of the apex of 

 the gland to the air when it pushes out from the pad of trichomes 

 within which its earlier development occurs. By that time how- 

 ever the dissolution of the epidermal cells is usually well along, 

 and in view of the positive evidence which we have advanced in 

 support of our explanation, it is scarcely necessary to saymore than 

 that it is probable that only very slight mechanical results may 

 be expected, and these only after the membrane has been partially 

 released by the disorganization of the cells. Such results can be 

 of only secondary importance. 



The three glands above described present in common the phe- 

 nomenon of the disorganization of the epidermal cells, setting free 

 the outer wall to form a chamber for the reception of the nectar 

 at the top of the gland. Excepting in Mamillaria at the beginning 

 of secretion only that which appears to be a free cuticle overtopping 

 the gland is in reality the whole outer cell wall or its remains. 

 The whole process is evidently the result of digestion of the uncu- 

 tinized cell walls, accompanied by digestion of the remaining con- 

 stituents. The inference seems justified that, even in Mamillaria, 

 when the cuticle alone is set free, this is permitted by a chemical 

 metamorphosis of the underlying cellulose, or of a part of it. This 

 explanation we believe to be equally applicable to other glands 

 in which a disorganization of the cell itself is not involved. Such 



6 Lloyd, F. E. and Ridgway, C. S., Cedar apples and apples. Ala. State Dept. 

 Agric. Bull. 39, 1910. 



