THE STRUCTUKES OF PITCHER PLANTS. 



61 



progressive increase towards the bottom of the pitcher is quite uniform, 

 and with their increase in size they have a varying relation to the hood. 

 Thus in a mature but unopened pitcher of N. Rafflesiana I made a set 

 of careful measurements of the glands and their hoods over the whole 

 surface, the results of which are embodied in the following table : — 



MEASUBEHENTS OF THE GLANDS OF A MATUEE BUT UNOPENED PITCHEB OF 

 NEPENTHES EAFFLESIANA. 



The measurements in the last two columns are only relative and not absolute. 



The epithelial cells and the intercellular canals have a corresponding 

 increase in their size. 



It will be seen from this table that the increase in size of the glands 

 from the lip of the pitcher downwards is gradual up to a certain point, 

 about a third of the way down. This zone clearly may be taken to repre- 

 sent the non-glandular surface of pitchers whose lids cover their aperture. 

 We may also conclude that at one time the lid of N. Rafflesiana covered 

 its mouth, but that some advantage being derived (probably that of a 

 subsidiary insect tx - ap, which it may readily be) from the modification of 

 the lid now seen, the disadvantage of the admission of rain-water had to 

 be made up for by an increase of the gland surface. This appears to me 

 to make it certain that the minute crescentic markings already described 

 on the non-glandular surface of N. phyllamphora are not retrogressions, 

 but structures only needing the necessity for development which N. Raffle- 

 siana has incurred. As all Nepenthes' pitchers have the lids of their 

 pitchers originally over their mouths, it is again in evidence that the 

 arrangements of N. Rafflesiana are an advance, and this is borne out by 

 the M»hole appearance and character of the plant, for it is said even to 



