THALLUS OF SPHAEROCARPOS DONNELLII AUST. IQI 
ments of initial cells of the apical region merge together in their development 
to form the broad marginal wing of the thallus ; while in culture the more 
rapid growth of the central portion of the thallus causes the separation of 
the tissue developed from each cell into separate lobes. 
In the plants grown in culture, the involucres are often broadly open 
at the tip and show various irregularities in form. Dorsal lobes were ob- 
served in several cases, and there are gradations between these dorsal lobes 
and the normal involucres. The Douins (6) also mention these peculiarities. 
This suggests the idea that the formation of lobes and that of involucres 
may be intimately connected, and that the form of the entire plant may 
depend rather strictly upon the environment. One might go even farther 
and suggest that there is an evolutionary relationship between some of the 
higher lobed or leafy liverworts and the various forms assumed by the more 
primitive types. There is at least a close resemblance. In Pellia epiphylla, 
according to Douin (4), of two middle lobes produced by the forking of the 
growing point, one is arrested in growth, while the other continues its 
development, and then a new lobe appears in the notch between them, 
thrusting to one side the lobe which has ceased its growth. The lateral lobes 
of many liverworts may be formed in this way. 
Plants grown under water by regeneration from involucres and from 
lobes cut off from the plant show the same abnormalities as those above 
described carried to an extreme, except that there is little or no branching 
and that sex organs are not abundant. The plant consists of a long almost 
cylindrical axis, bearing a few scattered and small leaf-like lobes. 
The following is a detailed "account of two of the plants studied as 
indicated above. They are typical of the history of all the other plants 
studied, so that it is needless to multiply examples. 
Plant no. i. Lobes a, h, c, e, and / (fig. 68 A, PI. XII) have already 
reached maturity, and do not change their position in the subsequent history 
of the plant; they may increase slightly in size. Lobe d is an example of 
a ''middle lobe," growing regions developing on either side of it. However, 
in the notch to the left of it, a single lobe forms {g, fig. 68 B), on only one 
side of which — between lob,es g and d — is there any further growth. In 
the notch between these two lobes growth proceeds in the usual way. On 
the other side of d, at first only one lobe — h — is visible (fig. 68 B), but 
another — i — soon makes its appearance (fig. 68 C), and finally comes to 
equal h in size. This sort of thing is of common occurrence, and indeed the 
formation of these little lobes exhibits the greatest variability as to size, 
shape, number, and time of appearance. The further history of this plant 
illustrates how the lobes are pushed into a lateral position, while new lobes 
arise at the apical region. In the last sketch (fig. 68 D), lobes h and i are 
approaching their mature size, and two small lobes have made their appear- 
ance simultaneously between them. On the other side of lobe d, meanwhile, 
two lobes {k and j) have developed at the same time (fig. 68 C) , and finally 
