54 THE WATERLILIES. 



fuse with one or both of the adjacent large bundles, leaving, with the 

 central one, five strong vascular trunks. Shortly the central and posterior 

 trunks unite, leaving four, and then the anterior and right trunks unite, 

 leaving but three traces. The left trunk may now join the fused right and 

 anterior, or these may remain separate and pass to opposite sides of the 

 gap in the vascular cylinder of the stem which is prepared to receive 

 them. This gap is identical in size and shape with those for the leaves 

 and stolons ; since a peduncle is a form of stem, this should probably be 

 called a ramular gap. The fused posterior and central trace passes in 

 over the lower edge of the gap and turns downward after the manner of 

 a central leaf-trace, with its phloem uppermost (innermost after turning 

 downward). Some analogy between the bundles of peduncle and petiole 

 would be desirable, but opinions on this would as yet be premature. 



THE LEAF. 



The three types of waterlily leaf mentioned on a previous page 

 have been designated by Arcangeli (1890, 6) hydrophylls (idrofilK), aero- 

 phylls (acrofilli} and aerohydrophylls (acridrojilli] ; the last includes all 

 of those commonly seen and familiarly known as lily-pads. It will be 

 more convenient, however, to speak in plain English of submerged 

 or water leaves, aerial leaves and floating leaves. The aerial type is 

 altogether exceptional. It occurs in N. odorata, alba, tuberosa, mexicana 

 and marliacea-chromatella when the plants are much crowded, or in 

 N. odorata minor where the rhizome is bedded in deep peat or sphagnum 

 from which the surface water entirely dries away in summer. In the last 

 case, specimens from Atco, N. J. have shown a few stomata on the under 

 side of the leaf near the apex, and such leaves are always firmer and 

 tougher in texture than floating leaves ; but other than this no difference 

 has been noted, and no further mention of them will be made. 



Floating leaves are present in all Nymphaeas, excepting N. alba, 

 when growing in deep, swift streams (which is a rare occurrence), and 

 perhaps in IV. amazonum submcrsa (Sagot, 1881) and N. oxypetala. A 

 mature flowering plant will have at one time from 4 of these in N. 

 tetragona to 6 or 8 in N. odorata or 10 to 15 in the large tropical species. 

 They are produced in rapid succession throughout the growing season, 

 and after functioning for a few weeks, turn yellow and decay. 



At the base of the petiole occur stipules of characteristic shapes 

 (Fig. 24). In Castalia the two " stipules are inserted on the edge of the 

 dilated pedestal of the leaf-stalk, and below the articulation of the latter ; 



