132 NATURAL SCIENCE. Aug., 



maintains that both cotyledons become leafy, but in any case the 

 embryo and early stages of growth of Cyclamen, which, whatever its 

 ancestry, is certainly not now aquatic, bear no great resemblance 

 to that of an ordinary monocotyledon. 



Mr. Henslow admits that more than one cause may produce the 

 same or analogous effect, and that while he attributes the total or 

 partial arrest of one cotyledon to an aquatic habit, a similar arrest 

 may arise from atrophy in consequence of the way in which the 

 embryo is folded in the bud, as Sir John Lubbock has shown to be 

 the case in Abronia arenaria. The fact, however, remains that not a 

 single undisputed instance is given of the arrest of one cotyledon 

 producing a monocotyledonous embryo in any aquatic exogen. The 

 wholesale degeneration to a quite undifferentiated embryo, as obtains, 

 for instance, in Utvicularia, does not help the theory. 



In the section headed " The Embryo " the author refers to an 

 observation of Van Tieghem's " that the angular divergence between 

 the cotyledon and the next new organ is i8o" (generally in endogeus), 

 or, if lateral, 90° (as in exogens). When this latter case occurs in 

 endogens, it implies that one cotyledon is due to an arrested condition 

 of the other of two opposite cotyledons ; so that the first leaf belongs 

 to a second pair decussating in position with the cotyledons. If the 

 first leaf be at 180°, then it would appear to have usurped the position 

 of the cotyledon that is lost ; but it is not strictly on the same level as 

 the cotyledon, inasmuch as the first leaf is completely included 

 within it, as may be seen in Asparagus, figured by Irmisch." Thus 

 whether the first leaf alternates with or is opposite to the cotyledon 

 the latter may be supposed to represent the survivor of a pair. No 

 instance is given of the alternate position, but Tamus communis is 

 quoted as a parallel instance to Asparagus, in which Dutrochet has 

 shown that the first leaf is exactly opposite the cotyledon, is very 

 rudimentary, and dies early, and he has no hesitation in calling it a 

 second cotyledon. The appendage to the embryo opposite the single 

 cotyledon of certain grasses, which several botanists regard as a 

 rudimentary cotyledon, is also instanced. 



We can, however, hardly accept these as proof of the origin of 

 the endogenous embryo from an exogenous by assumption of an 

 aquatic habit. In reflecting on the monocotyledonous embryo, we 

 are struck with the variety of form manifested, rather than by evidence 

 of arrest or degeneration. Of course in Orchideae we see the 

 degeneration, or want of differentiation, characteristic generally of a 

 more or less parasitic habit, and the same holds in Burmanniaceae ; 

 but in the Palms, Grasses, Scitamineae, and Bromeliaceae the 

 cotyledon is a complex structure, comprising two distinct, and often 

 clearly-separated portions ; one the sucker, resident in the seed, 

 dissolving and absorbing the store of endosperm, the other the sheath, 

 pushing above ground, becoming green, and protecting the developing 

 plumule. Many Irideae have embryos built on the same plan, but 



