1893. MONOCOTYLEDONOUS PLANTS. 135 



the seed. Mr. Henslow observes that the seeds of aquatic endogens 

 are generally exalbuminous, but as the hypocotyl or hypocotyl and 

 cotyledon are very much enlarged, there seems no more reason for 

 starvation of the primary root than in the case, for instance, ol 

 the oak. 



In the same section it is remarked that the arrest, presumably as 

 the result of an aquatic habit, is not confined to the primary root in 

 the Nymphaeaceac (where, by the way, there is a good stock of 

 albumen in the seed), but is continued into the first-formed leaves 

 which pass through various stages of development. Now, if Mr. 

 Henslow will refer again to the work on " Seedlings," he will find 

 that this gradation is quite the rule where the adult form of the 

 leaf is not a fairly simple one. See, for instance, the figure of 

 Clematis on p. 82, where the mature, much-divided form is only 

 gradually assumed. 



Attention is also drawn to the agreement between these and 

 occasionally other aquatic exogenous orders and endogens in several 

 points of anatomy. Such are the scattered closed bundles and 

 the large wood vessels which are probably "due to the par- 

 ticular degenerating effect of a watery habitat." As the author 

 himself observes, such appearances are by no means confined 

 to water plants among dicotyledons. Any habit which allowed a 

 relaxation in the effort for self-support, such as that of climbing, 

 might, and in fact does, have a very similar effect. It is pointed out 

 that the arrangement in Pepevomia is practically identical with that of 

 Commelina. Analogous degradations occur in parasites, Cynomovium 

 coccineum and Helosis guyanensis having the bundles " scattered through 

 the ground-tissue, exactly like any endogenous stem." 



As regards the comparison of the foliage of Victoria regia and 

 Sagiltavia, considering the close relation in form between the adult 

 leaves, orbicular-peltate and sagittate respectively, it is not remarkable 

 that the stages by which the normal form is reached should be 

 similar. 



From its resemblance to cotyledons " the prevailing ribbon-like 

 form of submerged leaves of endogens," seen also in Hippuris and 

 Callitriche, is regarded as of a more " embryonic " character than the 

 dissected type of submerged leaves of exogens, and the conclusion is 

 drawn " that those terrestrial endogens which still retain a linear 

 form (e.g., grasses), or ensiform (Iris), or other similar type of leaf or 

 rather phyllode, may be regarded as representing the ancestral sub- 

 merged ribbon-like form " ; while those with distinct lanceolate or 

 cordate blades, like Convallaria or Maianthemum, "represent the floating 

 types of existing aquatic endogens." The sagittate form seen in 

 many aroids has primarily arisen like the same forms in Nymphaeaceae 

 and Sagittaria from an aquatic habit. This reasoning seems based 

 on somewhat superficial characters. We find classed together as 

 representing one type leaves so totally different as the linear grass 



