EMBRYOLOGY 355 



is still obscure. The type of leaf seen in the cotyledon is repeated in 

 the " protophylls," but without definiteness of position or number upon the 

 enlarging tuber : their sequence is closed at last by the activity of the 

 stem-apex, close to which in time and in position the first root appears. 

 It is as though a rootless phase of morphological anomaly, initiated by the 

 parenchymatous swelling in the upper tier, were intercalated in the regular 

 embryogeriy of the Selago type, immediately after the origin of the cotyledon : 

 and after a period of digression the normal embryogeny were then resumed. 

 The swelling is associated in L. cernuum and inundatum with the entry of 

 a mycorrhizal fungus, which occupies the tuber : it must at present remain 

 uncertain whether or not this symbiotic state is the cause or a mere 

 concomitant of the tuberous condition : and what the relation of it to 

 the late appearance of the root ; but given the tuberous state, the other 

 anomalous foliar conditions readily follow. The proneness of the Lycopod- 

 embryo to such secondary swelling as contemplated is seen also in the 

 embryos of the clavatum-iy^Q : it is also shown by the repetition of such 

 swelling upon the roots in L. cernuum itself, as have been fully described 

 by Treub. 



The cernmim-tyTpe of embryo is shared by L. inundatum, but not in 

 its extreme form. It is this species rather than L. cernuum itself which 

 gives the link to Phylloglossum. The strobilus of the latter is like a very 

 simple strobilus of L. inundatum : this species, as is well known, perishes 

 in winter, excepting the tip of the trailing stem, which perennates. If 

 such a condition were still further prepared for, and condensed by the 

 formation of an adventitious protocorm in cases where the plant has been 

 fertile, or of a similar body as the product of direct apical growth where 

 the plant of the previous year was sterile, the condition of Phylloglossum 

 would be attained. It is interesting to note in this connection that Goebel 

 has found that adventitious protocorms are formed in L. inundatum, a fact 

 which strengthens the suggestion here made. 1 It would thus appear that 

 Pliylloglossum, so far from being a prototype of Lycopodinous development, 

 is more probably a specialised offset from it. I still adhere to my thesis as 

 stated in 1885, that "it is a permanently embryonic form of Lycopod." But 

 it may now be added that the characters which it repeats each year appear 

 to be those of a secondary rather than of a primitive embryonic type. 



And thus the embryogeny of the Eligulate Lycopods, so far as at 

 present known, conforms to a single central scheme with variations upon 

 it. The type of L. Selago, the only species of the "Selago" section of 

 the genus in which the embryo has hitherto been observed, is held to 

 be the most primitive, as it is certainly the simplest. The rest may be 

 held to be secondary variants on that type, due to changes for the 

 most part biologically intelligible. 



1 Bot. Zeit., 1887, Plate II., Fi^. 32. 



