WEST, ON PETALS OF FLOWERS. 23 
clearly traced as forming the tuberculoid elevation. A 
diagram (fig. 3) may serve to render my meaning clear. If 
the elevations were due to secondary deposit, we should see 
distinctly, as in the imaginary instance (fig. 4), the cell-wall 
continuous, and supporting an extraneous substance. 
Having satisfied myself, from this instance, that on the 
outer surface of vegetable cells, protuberances and hairs were 
not necessarily owing to external secondary deposit, I made 
very numerous examinations into analogous cases, the results 
of which have led me to believe that the views now held on 
this subject will require much modification to render them 
consonant with truth. I have met with no certain example 
of such, though one or two instances have occurred to me in 
which there might be a degree of doubt, from the top of the 
tuberculoid elevation being somewhat thicker than the sides ; 
in Galium mollugo it is so. But we need not hence assume 
that this is from secondary deposit, for it is certain that the 
cuticular cell-walls are not of equal thickness in all parts, 
and such an appearance may be easily explained without such 
an hypothesis. 
Hairs of much value for the purposes of our present inquiry 
occur in the throat of the pansy (Viola tricolor and varieties 
of V. lutea, fig. 11). They are large (35th im. long), knobbed all 
over ; these knobs, clearly produced by outward bulging of 
the cell-wall, are themselves irregular with lesser warty 
prominences, and towards the attached end of the hairs they 
subside into interrupted subspiral lines, equally due to 
folding. A sectional view of hairs from the throat of verbena 
(fig. 12) and petal of the musk-plant (fig. 13) shows that the 
dotted markings they possess arise in the same way. 
The radiating lines on the petals of geranium, &c., are 
likewise caused by corrugation. In petals removed from the 
scarlet geranium whilst the bud is still very immature, neither 
the papille, the radiating lines, nor certain so-called 
“hairs” arranged round the base of the papill, are present. 
But on examining petals from flowers advanced to about 
twenty-four hours from the period of opening, these are all 
found pretty well developed. Being still in a soft condition, 
the action of nitric acid diluted may be watched under -the 
microscope, causing evolution of the cell-walls and disappear- 
ance of the radiating limes or folds, with consequent 
appreciable increase in size of the papilla out of which they 
were formed. The petal of the larkspur shows the same 
facts equally well. When the eye is thoroughly familiarised 
with the objects, the optical appearances alone are almost 
sufficient to enable a confident opinion to be formed. 
VOL. VII. D 
