348 Groom. — On Thismia Aseroe ( Beccari ) 
in virtue of being the points at which the cytoplasmic strands 
connecting the hypha and nucleus attached themselves to the 
former. 
It will be seen that the chemotropically active substance 
and the substance which is absorbed as food by the hyphae 
have the same distribution, and are both manufactured in 
precisely the same spots and in the same proportion. This 
at once suggests that the two are identical, that one substance 
causes both effects. However this may be, the theory here 
given of the behaviour of the hyphae leads to the conclusion 
that the cortex and the sheath are strongly contrasted as 
regards their metabolic processes ; that in particular the 
cortical cells manufacture certain substances, or a substance, 
lacking nearly or entirely in the sheath. This contrast is 
indeed a matter of fact. For the young cortical cells contain 
a rich store of starch which only disappears when the hyphae 
enter, and which may reappear when the hyphae die : 
whilst the sheath-cells are always devoid of starch ; or 
occasionally some of the cells of the innermost layer of the 
sheath possesses starch ; and, precisely corresponding with this 
fact, it is not rare to find some of these innermost cells of the 
sheath possessing hyphae exactly like those of the exocortex, 
in which case the nuclei of these cells are larger and more 
deeply staining than the cells with only straight hyphae. 
Again, the sheath-cells are poor in protoplasm, but the cortical 
cells have an ordinary amount. 
The behaviour of the mycelia, then, strengthens the view 
that the nucleus of a cell is the centre of certain metabolic 
changes ; and, conversely, any observations tending to prove 
this action of the nucleus render the explanation above given 
more worthy of credence. Klebs’ observations, though not 
confirmed as of general significance by Palla and Acqua, show 
that the manufacture of one carbohydrate — the cell-wall— is 
influenced by the nucleus. Further, he demonstrated that in 
the leaves of Funaria hygrometrica pieces of protoplasm devoid 
of a nucleus did not make starch, though they were capable of 
assimilating. In young cells of higher plants the chromato- 
