DEVELOPMENT OF LEAVES AND STIPULES 65 



The leaves of water-plants are as a rule flat or 

 rolled, not folded. 



The consistence of the leaf exercises much in- 

 fluence, for thick, leathery, or fleshy leaves, such as 

 those of Mistletoe (Viscum), Aloe, many Crassulas, 

 Saxifragas, &c., naturally are as a rule flat ; some- 

 times rolled ; but rarely folded. Pinnate and trifoliate 

 leaves are generally folded. 



In Monocotyledons the leaf rises as an elevation 

 immediately below the growing-point, gradually sur- 

 rounding part of the stem, and highest at the point 

 opposite the opening. The ridge extends until it forms 

 a sheath more or less completely surrounding the stem. 



The leaves of Palms and Aroids develop in a 

 manner very unlike that usual among Dicotyledons. 

 The leal originally forms a continuous blade, which 

 is much folded, and subsequently divides. According 

 to Eichler, this is effected by a process of disorganisa- 

 tion at the edge of the fold. A similar process occurs 

 in the segmentation of the originally entire thallus of 

 species of Laminaria, a common genus of brown sea- 

 weed. Naumann (11), on the contrary, maintains that 

 the cells along the line of the fold detach themselves and 

 diverge from one another. I believe, however, that 

 Eichler's view is correct. 



