EMBRYOLOGY 361 
“righted” is then carried up together with the two leaves by the elong- 
ating hypocotyl, while the first root appears laterally at its base. The 
whole arrangement is relatively simple, but illustrates a slight degree of 
distortion of the apex, which is, however, temporary only. 
In the clavatum-type (Figs. 170, 186) the hypobasal tier is enlarged, 
and curved to one side, with correlative late differentiation of the epibasal 
region, and absence at first of localised intercalary growth. The orien- 
tation of the foot is not constant, but it is directed towards the chief 
source of nutriment, a fact which indicates its opportunist character. In 
the epibasal region the apex of the axis is clearly of central origin, 
between the two small but equal cotyledons, which appear relatively late. 
The root originates in a position corresponding to that of the former 
type. The whole embryo may be held to be a biologically intelligible 
modification of the Se/ago-type consequent on the underground habit of 
the large mycorrhizal prothallus. The enlargement of the haustorial foot 
leads correlatively to slow development of the epibasal region, while the 
first leaves, having no nutritive function, are not hurried on in their 
development so as either to distort or to produce correlative reduction of 
the apical cone. 
In the cernuum-type (Figs. 187, 188) the tuberous swelling is not in the 
hypobasal but in the epibasal region, and it profoundly disturbs its develop- 
ment. The biological cause of the swelling, which is extra-prothallial and 
liable to repetition, may be the intrusion of the symbiotic fungus which is 
present, or there may be some other reason for the tuberous development, 
associated as it is with the late’ origin of the root. But whatever the 
cause, the form is such as might be expected in a secondary tuberous 
modification of a green leafy shoot of a young Lycopod. The bulky 
development below, and the rapid enlargement of the assimilating leaves 
act correlatively in keeping the stem-apex inconspicuous. Its identity 
throughout the embryogeny of Z. cernuum itself is not yet demonstrated ; 
but in Phyloglossum the definitive apex of the shoot has been seen to 
coincide with the apex of the tuber (Fig. 189); it is therefore probable 
that in the embryogeny of JZ. cernuum the apex of the axis is present 
in the very young embryo in the usual position, but has escaped recog- 
nition owing to its correlative diminution. The protophylls would then 
be leaves of the normal type, altered in relation to the gouty habit of the 
axis which bears them, and disposed in an apparently irregular and isolated 
fashion upon the swollen axis. The root is long deferred, perhaps in 
relation to the mycorrhizal habit; but when it does appear, its relation to 
the leafy shoot is like that which it has in the other types of the genus. 
The normal leafy shoot and the root-system, thus delayed by the gouty 
interlude called the “protocorm,” ultimately continue their development 
as in other Lycopods. Thus the different types of the genus appear to 
start alike, and when established in the soil continue alike, but show 
divergent intermediate phases. The simple development of Z. Se/ago and 
