( 432 ) 
is the same, yet there exists a sort of antagonism between the two. 
So, for example, it is not unfrequently seen that when somewhere 
on a leaf a rootlet has been formed, immediately behind it a rhizome 
arises, or the reverse. ; 
The most striking case in this respect I observed with a leaf whieh 
had formed two rhizomes laterally of the leafstalk (which is a rare 
occurrence) one close above the other: at the other side of the leafstalk, 
exactly behind each of the rhizomes, a well-developed rootlet was 
found. 
Properly speaking this antagonism is already observed when a 
rootlet is formed on a rhizome in the ordinary way; it namely does 
not arise at some distance from the top, but quite close to it, so that 
sometimes the impression is given as if the top, of the rhizome would 
divide dichotomically, i.e. into two equivalent branches, whereas 
later one point develops into a rhizome, the other into a rootlet. 
So the two meristem-plasms are very nearly equal, until at a 
certain moment a division takes place. The principal cause of this 
division is, in my opinion, light. 
The rootlets can very well form and develop in light, but, if 
possible, they seek the shaded side or turn away from the light. 
Rhizomes, on the other hand, as well as prolifications, generally 
are formed at the bright side. 
Now taking into account that Norr *) has shown that a rhizome of 
Caulerpa forms rootlets at the upper side if this is shaded above 
and only illuminated from below, I think we have every reason to 
look upon the difference in the intensity of the light on both sides 
of the rhizome as the principal cause of the separation, which takes 
place in the at first homogeneous meristem-plasm, and hence also of 
the antagonism between rhizome and rootlet. 
That also internal causes play a part here, follows already from 
the fact that the rootlets as well as the leaves, are formed on the 
rhizome at distances which for each of them are pretty regular. 
A rhizome-top is even occasionally seen to dissolve entirely into 
rootlets, which proves that there can be no considerable difference 
of origin between them. 
So we are naturally led to the question: how do the leaves arise? 
In this respect I must restrict myself to a few hints, since the 
investigation of this point has not been completed vet. 
In the intact plant they arise either on the rhizome or as prolifi- 
1) Kinfluss der Lage, u. s. w. : Arbeiten aus dem botanischen Institut in Wiirzburg, 
Bd. III, 1888, S. 470. 
