burst and expand in spring, the leaves, at
whose bases the eggs have been deposited, instead of increasing in
length, enlarge at the base, and form a cell or cyst whose mouth is at
first closed by a red velvety-looking substance. If opened in this state
a nest of small greenish aphides is distinctly visible, and at a certain
period, or when they have acquired maturity, which is towards the end of
the summer, the mouth of the cell opens and the insects fly off to
inflict a similar injury upon the nascent buds of the year. In some
instances the leaves of only a portion of the circumference of a shoot
are affected, in which case, though a slight distortion may take place,
the branch is not prevented from elongating; but in others, where the
whole of the leaves around the shoot are converted into nidi, elongation
is prevented and distortion to a great extent takes place."

[525] See Cramer, 'Bildungsabweich.,' pp. 53, 64, for further
references.

[526] 'El. Ter. Veg.,' p. 124.

[527] Schlechtendal, 'Bot. Zeit.,' 1857, vol. xv, p. 67.

[528] On the subject of this paragraph the reader may consult A. Braun,
"Ueber abnorme Blattbildung," &c., in 'Verhandl.,' d. 35,
'Naturforscherversammlung;' Jaeger, 'Flora,' 1850. p. 481, tab. 4,
_Digitalis_.

[529] 'Org. Veget.,' i. p. 286.

[530] 'Bull. Soc. Bot. France, vol. viii, 1861, p. 710.

[531] 'Linnaea,' 1830, vol. v, p. 492.

[532] 'Mus. Senkenb.,' ii. p. 45.

[533] 'Bull. Acad. Roy. Belg.,' 1851, t. xviii. part i, p. 275.

[534] 'Bull. Soc. Bot. France,' vol. viii, 1861, p. 147.

[535] See Darwin, 'Variation of Domest. Anim. and Plants,' ii, 165.

[536] Gay, 'Ann. Sc. Nat.,' ser. i, 1824, t. iii, p. 44.

[537] See De Candolle, 'Mem. Legum.,' tab. 3, f. 1; Wyville Thomson,
'Trans. Bot. Soc. Edinb.,' 1851, July 10th; Berkeley, 'Gardeners'
Chronicle,' June 22nd, 1867, p. 654. A similar case is described by Dr.
Robb, in Sir W. Hooker's 'Journal of Botany,' 1841, vol. iii, p. 99,
with illustrative figures. The specimens there described were produced
at New Brunswick, where plum trees flower very freely, but seldom
produce ripe fruit. Dr. Robb's account is as follows:--"In the summer of
1839 I had an opportunity of watching the process of destruction among
the plums, and it was as follows--Before or soon after the segments of
the corolla had fallen off, the ovarium had become greenish yellow,
soft, and flabby. As the fruit continued to increase in magnitude, its
colour