CH. IV, 12] MONSTROSITIES OF STEMS 



201 



Related to these peculiarities of tissue development are the 

 TORSIONS, or close twistings sometimes found in plant tissues, 

 either stems or fruits. They are often prominent on trees 

 standing in burnt woods, or on fence rails, where the layers 

 of wood form closely wound spirals. 



Rather striking, and not uncommon, are PROLIFERATIONS, 

 well illustrated in the cases where a leafy shoot projects 

 from the tip of the fruit in Pear or Straw- 

 berry (Fig. 149). In Roses the stem occa- 

 sionally grows up through the center of a 

 flower and produces another, thus making 

 a "two storied" flower (Fig. 150), while 

 two-storied fruits, of similar origin, occur 

 occasionally in Apples. An incomplete 

 case is represented in the Navel Orange, 

 where the stem grows up between the seg- 

 ments of the fruit, and bears a smaller 

 orange, not, it is true, on the top, but 

 within the top of the main one. This case 

 is also of interest as showing that such 

 monstrosities can be propagated, for all 

 Navel Oranges are reproduced by grafting. 

 Stems, and therefore the stalks of flowers FlG 149 _ Pro . 

 and fruits, can potentially elongate indefi- liferous Pear. (From 

 nitely, and some special inhibitory influence 

 must ordinarily check their growth in flowers and fruits. It is 

 apparently the occasional failure, presumably by some acci- 

 dent, of this inhibitory stimulus, which results in proliferations. 



Among the commoner monstrosities are SUBSTITUTIONS 

 of one part or feature for another. Most people know that 

 green Roses occur; and a variety is grown in Botanical 

 Gardens on which the flowers are well-nigh as green as the 

 leaves. Formerly such cases were considered " re versions," 

 the petals being supposed to have returned to the state of 

 green leaves from which they were evolved. They seem 

 rather, however, to result from a substitution of chlorophyll 



