( 433 ) 
cations on the leaves. On the rhizome they arise on the upper side 
but, in opposition with the rootlets, always at a great distance (a few 
centimetres) from the top and consequently quite out of reach of 
the meristem-plasm there. I presume that their formation on the upper 
side is also determined by light, although this has not been proved yet. 
In unwounded leaves, and hence in the normal life of the plant, 
they are formed on full-grown leaves and then generally near the 
top, in cut leaves they very rarely occur near the top ; in these they 
as a rule arise on the lower two thirds of the leaf, preferably even 
on the lowest third part, but hardly ever immediately above the 
wound. So here also they arise out of reach of the meristem-plasm. 
The formation of the leaf begins with the appearance ofa very small 
white spot on the dark green organ. This rapidly grows out into 
a cylindrical, soon broadening appendix, which often remains entirely 
white until it has reached a length of one centimetre, after which 
it becomes green from below during further growth. The top remains 
white as long as the leaf increases in length, but turns green when 
growth is arrested, either by the leaf having reached maturity or by 
unfavourable external circumstances. 
In no case the formation of a leaf was preceded by the appearance 
of a large white spot with affluent streams of meristem-plasm. This 
leads to the conclusion that the young leaf derives its meristem-plasm 
evidently from the protoplasm of the whole neighbourhood; so a 
preferred direction of motion, as a consequence of a basipetal or 
acropetal impulse, cannot be detected. As a consequence of this each 
of these currents is so feeble, that it could not be observed with the 
hand-magnifier. So the formation of leaves appears to be independent 
of the descending current of meristem-plasm. 
In one case only I have seen white currents in connection with 
a young leaf; in a cut leaf I observed that a strong white bundle 
had differentiated itself, running close to the base of a young leaflet 
(prolification) that had arisen after the cutting. This was a little over 
a centimetre long and still as white as ivory. From its stalk six 
white streams passed into the leaf; they all ran in a basal direction 
and soon became absorbed in the white principal bundle. 
So these also obeyed the basipetal impulse; they had gradually 
formed during the development of the leaflet and so had not appeared 
as preliminaries to the formation of it, as is the case with the rootlets. 
Also the large white spot was absent here. 
Since the white currents in this cut leaf also flowed together 
at the base in order to prepare there the formation of a rhizome 
and of rootlets, we may infer from this that there is no essen- 
30 
Proceedings Royal Acad. Amsterdam. Vol. VII. 
