li8B Transactions. 



here associated with the L. cernuum type of pi'othallus. In these two 

 species it would seem to be much more than a mere "temporary sub- 

 stitute for a root-system delayed in its development " (Bower), for 

 it constitutes the plant-body for a whole season, attaining to a con- 

 siderable size, and even branching. Moreover, the fact that vascular 

 tissues develop within the main body of the protocormous rhizome 

 suggests that in origin it is not a mere parenchymatous swelling. On 

 these grounds it might be argued that the facts brought forward in this 

 paper lend weight to the theory which regards the protocorm as a very 

 ancient organ, possessing great phylogenetic importance. On the other 

 hand, there are certain considerations which suggest that too much 

 stress must not be laid upon the comparatively large size of the 

 protocorm in L. laterale and L. ramulosum. In the first place, the 

 manner of development of the protocormous rhizome in these species 

 lends credence to the idea that it is merely a physiological specialization 

 suited to carry the young plant over the dry season. The original 

 protocormous tuber, surmounted by its two protophylls, corresponds 

 closely with that in L. cernuum, &c. The rhizomatous extension of the 

 protocorm -^^ould seem to be, however, an added feature, to be inter- 

 preted apart from the original tuber. In its development it is 

 markedly distinct from the lattfer, being separated from it by a 

 constriction, and, moreover, it is initiated in L. laterale, and in 

 certain cases in L. ramulosum, subsequently to the decaying-away of the 

 prothallus, these two facts suggesting that a certain interval elapses 

 before it begins to develop. The manner of growth of the rhizome 

 strongly suggests that it is merely a specialized swelling, for it is the 

 swollen bases of each new pair of protophylls which add to its length, 

 and even the fully grown rhizome bears witness to the manner of its 

 development in the arrangement of the jDrotophylls in two more or less 

 obvious rows on its dorsal surface and in the median groove running the 

 length of the rhizome on the ventral side. Also, in L. cernuum a some- 

 what similar lateral extension of the protocorm has been observed to take 

 place, although to a less important extent, and this extension would seem 

 to be a SAvelling distinct from the original tuber. There is a strong sug- 

 gestion that the Lycopod protocorm is more plastic than an ancient and 

 highly primitive organ would be expected to be, and that stress' must 

 not be laid from a phylogentic point of view upon the fact of its normally 

 large development in L. laterale and L. ramulosum. 



In the young plant of L. cernuum the vascular strand from the- 

 developing stem-apex takes a course through a corner of the protocorm. 

 Tlie short region of the latter which lies between the stem and the first- 

 root apices may possibly be regarded as the rudiment of the stem-axis, 

 retarded in its development and pushed out of its place through the- 

 intercalation of a tuberous stage. It is to be noted that the stem-apex 

 and the first root always originate close together, and on the side of 

 the protocorm farthest away from the prothallus. In L. laterale, and 

 in L. ramulosum also, the stem and first root arise at the growing end 

 of the protocorm, sometimes in close juxtaposition, though generally 

 farther apart than in the case of L. cernuum. Here, too, it is possible 

 to look upon that region of tlie protocorm through which the vascular 

 strand passes as the rudiment of the stem-axis, very much postponed in 

 development, and varying in size, owing to the intercalation in the 

 embryogeny of the abnormally larce rhizomatous swelling. 



On the whole, the present writer inclines to the opinion that the 

 large size and other abnormal features of the protocorm of L. laterale 



