300 Evans .— Vegetative Reproduction in Metzgeria. 
acquired the characteristics of maturity, it first goes back into an embryonic 
condition, and then undergoes the necessary cell divisions. The new plant 
formed in this way does not at first show the peculiarities of an adult 
individual, but begins its life in one of the juvenile or embryonic stages of 
the species. In those Lejeuneae, for example, where the mature plant is a 
leafy shodt with underleaves, the regenerated plant is very often a leafy shoot 
without underleaves or even a thallus, upon which a leafy shoot subsequently 
develops. Under conditions which are considered normal for the growth 
of a species, the mature cells are in some way prevented from exercising 
their latent power of division, and regeneration does not take place. This 
is apparently due to a kind of antagonism w r hich exists between the apical 
region and the other parts of the plant. In other w r ords, the apical region, 
where active growth is normally going on, exerts an inhibitory influence 
upon the other cells, preventing or making difficult their independent 
development. It is probable that this influence is connected with nutritive 
processes in such a way that all the food available for growth passes to the 
apical region, leaving none for the other cells. 
The influence just described can easily be removed by dissecting off 
a leaf or a mature piece of a thallus. If the leaf or thallus fragment is then 
placed under conditions favourable for growth, regeneration ought to be 
induced. Among those who have carried on successful experiments along 
this line, Vochting (’ 85 ) and Schostakowitsch (’ 94 ) may be especially 
mentioned. Vochting confined his attention to Marchantia and Lunularia , 
but Schostakowitsch selected his material from all groups of the Hepaticae. 
Regeneration is sometimes brought about in nature by a very similar 
process. In certain leafy species, for example, the separation of some of 
the leaves from the axis may be considered a perfectly normal occurrence. 
This is seen especially well in various tropical Lejeuneae, such as Cheilo- 
lejeunea decidiia and the species of Rectolejeunea recently described and 
figured by the writer (’ 06 ). The deciduous leaves, under suitable conditions 
for growth, give rise to new plants by regeneration. 
In some of the gemmiparous species of Metzgeria , a similar antagonism 
between the apical region and the cells capable of developing gemmae is 
evident. When this is the case no gemmae are produced so long as the 
apical growth continues vigorous. It is only when the apical cell dies or 
when its activities are lessened or stopped altogether that the formation of 
gemmae begins. The death of the apical cell apparently takes place 
regularly in M. oligotricha , and brings about not only the production of 
gemmae, but also the formation of postical adventive branches, which seem 
to require similar conditions for their development. The gradual diminution 
in the divisions of the apical cell, leading eventually to complete suppression, 
is a regular process in the specialized gemmiparous thalli of M. fruticulosa , 
but it also takes place in gemmiparous branches which are not specialized, 
