4.56 ABORTION OF THE 
nodes are so shehtly developed that the leaves are 
closely crowded in tufts or rosettes. When this short- 
ening of the stem (acaulosia) occurs, without other 
considerable change in other organs, the deviation is 
classed under the head of variation rather than of 
monstrosity; and, indeed, in very many plants, this 
arrested growth of the axis is the rule rather than the 
exception. When occurring in an abnormal manner, 
atrophy of the stem is most frequently attended by 
other more or less grave alterations in other structures ; 
thus Moquin-Tandon' cites an instance of Campho- 
rosma monspeliaca, wherein the stems presented the 
form of very short, hard, woody tubercles, thickly 
clothed with deformed leaves, and imvested by a vast 
number of hairs, longer and more dense than usual. 
A similar deformity sometimes occurs in an Indian 
species of Artabotrys ; im these specimens the branchlets 
are contracted in length, and bear numerous closely 
packed scaly leaves, densely hairy, and much smaller 
than ordinary. 
Spines and thorns may be looked on as atrophied 
branches, and seem to result from poorness of soil, as 
the same plants, which, in hungry land, produce spines, 
develop their branches to the full extent when grown 
under more favorable conditions.” 
In the birch an arrest of development in some of the 
branches is of common occurrence. ‘The branch sud- 
denly ceases to grow in length; at the same time it 
thickens at the end into a large bulbous knob, from. 
which are developed a profusion of small twigs, whose 
direction is sometimes exactly the reverse of that of 
the main branch. (See p. 347.) 
The branches of the common spruce fir, especially 
the lateral ones, when attacked by a particular species 
of aphis, are very apt to be developed into a cone-like 
excrescence.° 
1 «Hl. Ter. Veg.,’ p. 182. 
2 Spinose arbores cultura sepius deponunt spinas in hortis, ‘Linn. Phil. 
Bot.,’ § 272. 
3 Mr. Selby, in his ‘History of British Forest Trees,’ p. 465, gives 
