26 WEST, ON PETALS OF FLOWERS. 
Round the margin of the cuticular petalline cells of pelar- 
gonium (fig. 14), geranium, in all its species, so far as I have 
had the means of ascertaining (fig. 5), periwinkle, Vinca 
major (fig. 15), nemophila, aiid others, are little dentate pro- 
cesses, appearing, when viewed from above, as if pointing 
inwards towards the centre of the cell to which they belong. 
Seen in profile, it becomes evident that they do not project 
freely into the cavity of the cell, nor outwardly, but are 
indeed in close apposition with the cell-wall. These are 
really pats of internal secondary deposit, as is proved by 
watching the progress of their development and the action of 
nitric acid. Such little pats are common at the most pro- 
jecting part of the curves of sinuous petalline cells; the 
curves sometimes become angular, and this appearance is 
much increased by the deposit. In the clove-pink (fig. 16) 
this secondary deposit is laid down more irregularly; in the 
petals of the white poppy (Papaver somniferum, fig. 17) and 
St. John’s wort (Hypericum) they form an imperfect spiral. 
Another case of what will be probably found to be due to the 
same cause is met with in some petals just within the point of 
the papilla; this is the case in Orchis maculata, and in Vinca 
major (fig. 15). 
It would be interesting to ascertain if, when papille occur, 
we may expect to find them in other species of the same 
genus, and in allied genera; also to what degree they retain 
similar forms and markings. My observations are not suffi- 
ciently numerous to found safe generalizations upon, but 
they appear to favour the idea that such may be the case. 
In conclusion, it may be well briefly to recapitulate the 
propositions here sought to be established. They are— 
lst. The prolongation of the outer cell-wall of the cuticle 
of petals into mammillary protuberances as a usual con- 
dition; such elevations being, with rare exceptions, most 
marked on the inner surface, and being hairs in a more or 
less rudimentary condition. 
2d. That the markings on the parts here named (which 
may be divided into two kinds, lines and dots, though 
examples of an intermediate nature occur) are both caused by 
corrugation of the cell-wall, and not by external secondary 
deposit upon it. 
Note.—The dots here spoken of on some petalline cells and many vege- 
table hairs have a special interest, from the light they throw on the trae 
nature of the markings of the Diatomacex. In each we have minute spots, 
but in the first named they are above, in the latter below the general level of 
the surface. It is as unphilosopiical then to apply the term “ cellules” to 
the markings of a diatom, as it would be to give it to the tuberculoid dots 
in question. 
