456 ABORTION OP THE 



nodes are so slightly 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 Gampho- 

 rosma monspeUaca, wherein the stems presented the 

 form of very short, hard, woody tubercles, thickly 

 clothed with deformed leaves, and invested by a vast 

 number of hairs, longer and more dense than usual. 

 A similar deformity sometimes occurs in an Indian 

 species of Artahotrys ; in 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.' 



' El. Ter. Veg.,' p. 132. 



' Spinosce arbores cttUura soepiiis deponunt spinas in hortis, ' Linn. Phil. 

 Bot.,' 272. 

 = Mr. Selby, in hia ' History of British Forest Ti-eee/ p. 465, gives 



