158 



PRINCIPLES OF PLANT-TERATOLOGY. 



(Pinus ponderosa) . When the staminate shoots were 

 pruned, the scale-leaves, scattered on the stem, became 

 hypertrophied and developed as foliage-leaves, resem- 

 bling, though not quite identical with, the primordial 

 leaves of the plant, and comparable to the scattered 

 leaves occasionally produced on young shoots of the 

 larch (Larix). He regards them as atavistic, and the 

 twigs bearing them may be compared to the permanent 

 condition such as obtained in Leptostrobus and Laricop- 

 sis, ancestral forms found in a fossil condition in 

 Siberia and the Potomac, the former standing in the 

 ancestral line of the Pines and the latter in that of 

 the Larches. 



5. Phyllody op Tendrils. — The tendril of the Legu- 

 minosse, Fumariaceas, and some Cucurbitacege affords 

 an instance of a foliage-leaf which has become greatly 

 reduced in area of surface and otherwise modified for 

 climbing purposes. Reversions to the original con- 

 dition are sometimes met with. Penzig observed leaves 

 of the narrow-leaved everlasting pea (Lathyrus syl- 

 vestris) in which some or all of the tendril-branches had 

 become changed into leaflets, giving rise to impari- 

 pinnate leaves. In the yellow vetchling (Lathyrus 

 Aphaca) there are normally no leaflets formed, these 

 being replaced by the tendril. Moriere and Vetter 

 describe a form unifoliolaius in which the tendril is 

 replaced by a small linear-lanceolate leaflet. Mann 

 induced artificial foliation of the tendrils in the garden 

 pea (Pisum sativum). The tendrils of the bryony 

 (Bryonia dioica) are also cited as occasionally changing 

 back into foliage-leaves. JNaudin describes and 

 figures very interesting transitional forms between 

 tendrils and foliage-leaves in Cucurbitaceae, which 

 prove, in the best possible way, what their real nature 

 is (fig. 42 a and b). 



6. Phyllody of Thokns.' — The development of thorns 

 and spines is in the majority of cases the result of, 

 and an adaptation to, a dry habitat, and at the same 

 time probably a protection against animals ; it is, in 



