254 Dr. J. E. Planchon on the Parasitism of Osyris alba. 



XXV. — On the Parasitism of Osyris alba. 

 By Dr. J. E. Planchon*. 



In 1847, an English botanist, Mr. Mitten, detected that the 

 roots of Thesium adhere by means of suckers to the roots of 

 various plants. A fact like this was very surprising in plants 

 with green leaves ; for M. Decaisne had not then made known the 

 similar parasitism of the Rhinanthacese. The species of Thesium 

 belonging, as is well known, to the family Santalaceae, analogy 

 would lead to the supposition of a similarly parasitic life in 

 Osyris alba, which represents in the south of Europe the most 

 highly developed type of this order. Urged by M. Decaisne, 

 Dr. Planchon sought to verify this presumption; but, for 

 two years, his attempts were vain. The fragile roots of Osyris 

 alba leave attached to the nourishing roots the organs of suction 

 which alone could reveal their parasitic character. This year, 

 more fortunate, he has been able to make numerous observations 

 on this subject, the most striking results of which he communi- 

 cates to the Academy. 



Osyris alba lives parasitically upon numerous herbaceous or 

 woody plants (all perennial) belonging to different families of 

 the class Dicotyledons. It implants its suckers upon the roots 

 or the rhizomes which it meets with, not sparing even its own 

 species. Ailanthus, Rhus Coriaria, Ulmus campestris, Jasminum 

 fruticans, Pinus halepensis, Rosa canina, Silene italica, Lychnis 

 dioica, Rubia peregrina, all the inhabitants of hedges or copses, 

 are subject to its attacks. 



The roots of Osyris arise scattered upon the long rhizomes 

 which creep in the soil at a small depth. They consist of slightly 

 branched fibres, the diameter of which does not exceed 2 milli- 

 metres. Their organs of suction are a kind of hemispherical or 

 conical cup, the dimensions of which vary from the size of a 

 pin's head to that of an acorn cup. The same radical fibre may 

 furnish one, two, three, or a whole series of cups. These em- 

 brace closely with their circumference the nourishing root. 

 They implant themselves there, moreover, by means of a fleshy 

 process or papilla, of cylindrical or discoid form, which penetrates 

 the foreign root, sometimes stopping short in the thickness of 

 the cortical parenchyma, sometimes insinuating itself between 

 the bark and the wood, sometimes, but more rarely, penetrating 

 as far as the ligneous tissue. 



The papilla of suction is formed in all cases by a cellular 

 tissue, which is separated into two zones by a sheath of monili- 

 form pitted vessels. The interior is a medullary zone, the exte- 

 rior the cortical parenchyma. The contact of the papilla with 

 * Translated from the Comptes Rendus, July 26, 1858. 



