274 SOUTH AFRICAN FLOWERING PLANTS. 



in a point; a similar flat one with a blade at the top, 

 of the shape of an arrow-head, as in lUchar'dia ; thirdly, 

 the same with the space between the lower points 

 filled in, so making a peltate, or shield-like leaf. 



In a common English plant, called the "Arrow- 

 head," from the shape of the leaf-blades, we discover 

 that the first kind (without any blade) occurs when 

 submerged in deep water, the long, narrow form being 

 caused by its growing, or being " drawn " up, towards 

 the light above. 



When it can reach the surface, the blade begins to 

 be formed, and is oval in shape ; soon, however, it 

 develops projections below, looking like a " spear "- 

 head, and is said to be hastate. These points grow 

 downwards, making a sagittate, or arrow-shaped blade. 



The further condition of a peltate blade does not 

 occur in this plant, but does in other genera, as 

 Cala'dium. 



Another ^-point is important ; namely, that the flat 

 linear leaf is really the leaf-stalk, or phyllode, and as 

 the veins run parallel to one another in leaf-stalks, 

 this accounts for the general description applied to 

 Monocotyledons of having " parallel or straight- veined " 

 leaves. The importance of this is seen in the fact that, 

 besides several plants of the Aroidcce showing these 

 differences, much the same occur in the Water-lily 

 family {Nymphmaceoi) of Dicotyledons. 



There are, in fact, many more points of resemblance 



