1784 



TERATOLOGY 



known examples. The gall-gnats among the true flies 

 (Diptera) also produce a large variety of malforma- 

 tions, of which the cone-like galls resulting from de- 

 formed buds of the willow and the goldenrod are best 

 known. Plant lice (Aphidae) are responsible for the 

 large smooth red galls on the petiole of sumachs, and 

 for the flattish serrated galls on elm leaves. The fusi- 



2484. Dahlia leaf 



stratine the branching i 



form galls on stem of goldenrod and asters is caused 

 by the larva of a moth. In addition to true insects, the 

 raites produce almost as great a variety of galls, pouch- 

 galls and leaf-rolling being especially conspicuous. The 

 cause of these deformities is sometimes the chemical 

 stimulus produced by the injection of substances 

 ("poisons") at the time of egg-laying by the parent, in 

 which case the gall develops around the egg; sometimes 

 it is the mechanical stimulus due to movements of the 



TERATOLOGY 



larva, together with the chemical stimulus from its va- 

 rious excretions, in which case the gall develops after 

 the hatching of the egg. 



chi„g 



li-av 



pelo 



ual flowers. Example of 



certainly cooperate. 



not infrequent, and its cause 

 is unknown. "Four-leaved" 

 clovers offer well-known ex- 

 amples, and the normal num- 

 ber of leaflets is often in- 

 creased to six or even more. 

 Fig. 2484 illustrates leaf- 

 branching in the dahlia. 

 Branching in the plane of 

 flattening, both in foliage 

 leaves and petals, has also 

 been observed, and the 

 branch described as an "out- 

 growth." 



6. Peloria. When usually , 

 irregular flowers, such as ' 

 those with some spurred or 

 saccate petals or sepals, de- 

 velop all the parts of each 

 set alike, thus becoming 

 radiajly symmetrical, the 

 phenomenon is called pe- 

 loria. It was first observed 

 by Linnaeus in Linaria vul- 

 garis. Fig.2485, and the term 

 peloria, derived from the 

 Greek word for monster, 

 was given by him. Flowers 

 often become peloric on ac- 

 count of changes in their re- 

 lations to light, but other ca 



reverse change, by which radial flowers become zygo- 

 morphic, occurs in many Compositae when the corollas of 

 disk florets become strap-shaped, as in the cultivated 

 asters and chrysanthemums, but no notice seems to 

 have been taken of it as a malformation. Sometimes, 

 on the contrary, all spurs fail to develop. Figs. 2486-7. 



in. Transformation of Organs: i. e., alterations 

 more profound than those of form, which result in the 

 production of organs different from those which 

 normally occupy the position; often called metamor- 

 phosis. (The term substitution would be preferable at 

 present, because non-committal as to processes and 

 causes.) It is common to speak of progressive and 

 retrogressive metamorphosis, 

 but these terms involve as- 

 sumptions as to the origin of 

 foliage leaves and floral parts 

 which are not .iustiflable in 

 the present state of knowl- 

 edge. Transformations 

 chiefly in the region of the 

 flower, though they are not 

 fouiiil exclusively there. Ex- 

 anii>l.s are to be "found in the 

 (lev.-lopnient of 

 leaves or leaf- 

 lets as tendrils 

 (Fig. 504); of 

 sepals as petals; 

 and of petals as 

 stamens or pis- 

 tils. These- 

 transformations 

 are usually more 

 or less imper- 

 fect. On the 

 other hand, the 

 pistils and sta- 

 mens often de- 

 velop as petals 

 (Fig. 367), and 

 many double 

 flowers owe 

 their fulness 

 chiefly to such transformations, though other changes 

 may cooperate as noted above. Fig. 2488. Petals 

 may develop as sepals, bracts, or even imperfect foliage 

 leaves, while sepals and bracts frequently become foil 



