12 ALISMACEAE [ch. 



the plant in its submerged state sometimes occurs when weeds 

 are being cleared out of a river. The semi-transparent leaves 

 which have been regarded by some authors as purely petiolar^, 

 while others consider them to represent the entire leaf in a 

 rudimentary form^ often grow to great lengths; the present 

 writer has measured one as long as 6 ft. 9 in.^ from the river 

 Cam. As many as twenty ribbon-leaves are said to be some- 

 times borne by a single plant in very deep water*. The 

 streaming ribbon-leaves of Sagittaria and other submerged 

 plants with the. same type of foliage, have a singular beauty 

 when seen forming, as it were, a meadow beneath the surface of 

 the water, moving in the current in a way that recalls a field 

 of wheat swayed by the wind. 



The ribbon-leaved form of Sagittaria sagittijolia is generally 

 sterile, but the appearance of flowers at this stage is not un- 

 known^. In moderately shallow water, transitions between the 

 aquatic and aerial types of leaf may be observed. The first- 

 formed leaves are band-shaped and submerged, while later ones 

 begin to spread at the apex so as to form a distinct lamina. 

 Some of these transitional leaf-blades, which are of lanceolate 

 to ovate form, float on the water. In another species, Sagittaria 

 natans^, these floating leaves represent the mature type of leaf 

 and are associated with the inflorescence, but, in the Aiyowhead 

 itself, yet a third kind of leaf is produced. The abbreviated axis 

 gives off, in succession to the leaves with floating blades, others 

 whose petioles rise into the air and whose laminae become more 

 and more sagittate at the base, until the typical arrowhead form 

 is achieved. The band-shaped leaves, though characteristic of 

 the plant which is wholly or partially submerged, are not con- 

 fined to it. The first leaves produced by a germinating seed or 

 tuber are ribbon-like, whether the plantlet develops in air or 

 water. At the end of May, the present writer has found young 



1 Candolle, A. P. de (1827). 2 Qoebel, K. (1880). 



^ A length of two metres (6 ft. 6 in.) has been recorded by Costantin, 

 J. (1886). 4 /^/V. (1886). 



5 Kirschleger, F. (1856). ^ Wachter, W. (1897I). 



