i02 MR. B. CLARKE ON THE EMBRYOS OF ENDOGENS 



iiiurina the radicle is readily discernible lying in a canal directed obliquely towards the 

 apex of the seed. 



Although the germination of the Endogens is as yet known only in part, the subjoined 

 instances of the exorhizal character occurring among them will, I believe, lead to the 

 anticipation that the endorhizal is the exception rather than the rule, as most of those 

 families in which the germination is unknown scarcely differ from one or other of the 

 following, in which the primary radicle, as far as my observations have extended, is 

 strictly exorhizal : — lAliacete, Dioscoreacece, Juncaginecs, Alismacece, Butomacew, Iridece, 

 Amarylli(le(B, Orchidece, Palmacece, Aracece, Typhaeece, and Eriocmilonece *. 



The inquiiy relating to the position of the first leaf of the plumule originated in 

 having observed that in the Graminacece the first leaf of the plumule is next the coty- 

 ledon, whilst in all other Endogens I had seen germinating it was directly away from the 

 cotyledon, so as to be alternate with it, as in the ordinary genera of Liliaceous plants. 

 For some years this phenomenon had appeared inexplicable, but fiu'ther comparisons 

 have led to the conclusion that the suggestion of L. C. Eichard, as regards the embryo of 

 the Graminacece, viz. that the apparent cotyledon is in reality an enlarged radicle, is the 

 only practicable explanation of this departm-e from the regularly alternate position of the 

 leaves of the embryos of the Endogens. But as objections exist to regarding the apparent 

 cotyledon of the Grarniinacece as the radicle or a part of it, it may with equal propriety be 

 compared to the enlarged cauliculus occm-ring in exogenous plants, or to the cormus as 

 occurring in endogenous plants, and then the first leaf of the plumule will be the coty- 

 ledon, containing within it the leaves of the plumule occupying then- usual alternate 

 position. For the purpose, however, of being more readily understood, I shall, with 

 Richard, stiU call it a radicle, though at first sight this view does not appear at all pro- 

 bable ; but yet the position of the first leaf of the plumule next the apparent cotyledon in 

 Graminacece and Cyperacece (fig. 20 c) appears otherwise an anomaly not to be accormted 

 for. But admitting that the cotyledon, as at present generally understood, is either an 

 enlarged radicle or a cormus, the steps by which such an inference may be arrived at 

 form an almost unbroken chain. 



Beginning, for example, with CauUnia, Naias, and Fotamogeton, we find that the first 

 leaf of the plumule alternates with the cotyledon, being directly away from it ; and the 

 embryo does not otherwise differ materially from those of Orontiacece, Aracece, and 

 liiliacece, excepting that the plumule is situated higher up, in consequence of its radi- 

 cular portion having become elongated. But in Zannichellia we find a commencing 

 alteration in structure ; the radicle has become more enlarged, and a partial ridge is 

 formed on its upper part round the base of the cotyledon (figs. 4 & 5) ; but no further 

 difference is observable, as the first leaf of the plumule is directly away from the coty- 

 ledon, as in Naias and Potamogeton. 



Passing on to Rttppia, we find the cotyledon depressed and lying almost horizontally on 

 the now enlarged radicle, which forms a shallow ridge surrounding it, so that it appears 

 to lie in a furrow on its upper surface. This ridge is found to be divided into two parts ; 



* The primary radicle, as afterwards described, becomes suddenly arrested in its growth, but, as far as it developes, 

 it is not endorhizal. 



