Miscellaneous. 209 



MISCELLANEOUS. 

 Note on the Hop-fly. By Francis Walker, Esq. 

 The alternate generation of Aphides, or the succession of winged to 

 wingless broods, is an interesting part of their history, and the more 

 so, for its consequence in many species is the migration and change 

 of food of the winged insects. Thus the Hop-fly (Aphis Humuli) is 

 hatched on the sloe, and the second generation passes thence to the 

 hop, which is much exhausted by the third and fourth broods, but 

 these decrease in number or disappear after awhile, and then the 

 Aphis returns to the sloe. 



On the Parasitical Nature of the Rhinanthaceae. By J. Decaisne. 



Since DeCandolle established by ingenious observations and accre- 

 dited by the authority of his name the separation of parasitic plants 

 into two groups, physiologists have generally admitted it as a well- 

 established law. It is known in fact that the phanerogamous 

 plants which are parasitic upon the stems of other vegetables have 

 green leaves, while those upon roots do not possess true leaves, con- 

 tain no green colouring matter, but are generally of a whitish, yel- 

 lowish or violet colour : in other words, they appear blanched or 

 sickly when compared to other plants ; their leaves, or the scales with 

 which their stems are provided, are generally without epidermic 

 pores. The absolute character of the law advanced by DeCandolle 

 has however been recently modified by the observation of Mr. W. 

 Mitten of a plant (Thesium Linophyllum) parasitic upon roots and 

 nevertheless provided with green leaves. 



The observation of Mr. Mitten immediately called to mind a fact 

 I had long noticed, that is, the impossibility of cultivating plants be- 

 longing to the group of the true Rhinanthacece. Wishing to intro- 

 duce into cultivation the purple cow- wheat (Melampyrum arve?ise), I 

 frequently sowed the seed, which however all perished a few days 

 after their germination without my being able to account for this want 

 of success. The same applies to species oiPedicularis and Euphrasia : 

 removed with care from the field and transferred with every possi- 

 ble caution into our gardens these plants soon dry up, in a few 

 hours they become black and so brittle that they appear to have been 

 scorched. Bearing in mind these facts, the question suggested itself, 

 whether the uncultivable Rhinanthacece might not be parasitic plants ; 

 in fact, their rapid death in our gardens and their injurious effects 

 upon the neighbouring plants, a fact well known to cultivators, led me 

 to suspect their parasitic nature. The observation which I have the 

 honour to bring before the Academy settles this question. The 

 species of Alectorolophus, Melampyrum and Odontites are true para- 

 sitic plants which fix themselves to the roots of grasses, shrubs or 

 even trees by numerous suckers. These suckers are arranged on the 

 branched and delicate rootlets of Melampyrum in the same manner 

 as on the filaments of Cuscuta ; the parasitic rootlets are in close 

 contact with the young roots of the plants upon which they feed ; 

 the point of contact is indicated by a swelling. 



Ann. 8f Mag. N. Hist. Vol. xx. 15 



