650 DK DICKSON ON DEVELOPMENT OF 



is no trace of a second cotyledon is quite evident from examination of the 

 mesial sections.* 



P. grandiflora, Lam. (Plate XXX. figs. 41-42). 

 After examining the embryo of P. vulgaris, I was curious to ascertain whether 

 there was any difference between it and that of this species, which is so nearly 

 allied to P. vulgaris that some botanists are disposed to combine them together ; 

 and I was gratified to find embryonic characters by which they may readily be 

 distinguished from each other. In front view (fig. 41), the embryo of P. grandiflora 

 (which is about the same size as the last) exhibits a single cotyledon having about 

 the same relative length to the whole as that of P. vulgaris. The base of the 

 cotyledon, however, is found almost completely to surround the extremity of the 

 embryonic axis, so that hardly a vestige of the plumule is to be seen from the 

 outside; and on back view (fig. 42), the tip of the cotyledon is seen to be 

 constantly and deeply bifid.f The first peculiarity is, so far as I have seen, 

 absolutely distinctive between this embryo and that of P. vulgaris ; while as to 

 the second one, it is, as I have just mentioned, only in very rare cases that the 

 cotyledon of P. vulgaris is bifid at its extremity. These embryonic characters, 

 combined with some other remarkable differences (such as the number of adven- 

 titious buds produced at the bases of the outer leaves of the autumn-rosette — 

 in P. vulgaris, usually only one in the middle line of each leaf; in P. grandiflora, 

 a considerable number in a single transverse row), go far, in my opinion, to 

 establish the validity of the claim of P. grandiflora to be ranked as a species.]; 



P. lusitanica. 



With regard to the very minute embryo of this species (about g^th of an inch 

 in length), I need not say much, beyond confirming the statements of St Hilaire 

 as to there being two cotyledons. These are relatively considerably shorter than 

 the single one of P. vulgaris or P. grandiflora. I have to note the presence of a 

 trace of albumen in the seed here. 



* Tkeviranus' figure of the embryo from the seed is somewhat faulty, from the cotyledon 

 being represented as considerably too short in proportion to the radicle, and from the absence of anv 

 indication of the rudimentary plumule. There is also no indication of the plumule in his figures of 

 the earlier stages of germination, the result, doubtless, of imperfect observation (loc. cit. t. iv.). 

 He also makes a curious blunder in describing the apex of the embryo as pointed towards the hilum 

 of the seed (loc. cit. p. 442), the fact being that in. this, as in all anatropal seeds, the apex of the 

 embryo points away from the hilum, the radicle being directed towards it. This mistake is probably 

 due to the circumstance that there is often a projecting portion of the testa at the chalazal extremity, 

 which is apt to be mistaken for the somewhat similar projection at the hilum. 



f I think it not improbable that back views of this embryo may have had something to do with 

 the statement found in most of the books, that there are two " cotyledones brevissimae " in Pinguicula. 



I I should mention that a very brief statement, by me, of the differences between the embryos 

 of P. vulgaris and P. grandiflora, has already appeared in the report of a meeting of the Dublin 

 Microscopical Club (" Quarterly Journal of Microscopical Science," viii. pp. 121-2). I now take this 

 opportunity of describing them in greater detail, and with figures. 



