80 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Development and Structure of Orobanche in a young stage, and 

 of its suckers.* — M. M. Hovelacque describes tbo development and 

 structure of Orobanche, taking as bis type 0. omenta. 



In a very early stage tbe Orobanche appears on tbe bost as a circular 

 or curved spot. Tbe parasite has penetrated tbe fibrovascular bundles 

 of its bost, and consists of a single unramified sucker which now begins 

 to enlarge rapidly. When more developed, tbe young Orobanche appears 

 as a hemispherical swelling ; it is, however, impossible to distinguish 

 growing point, axis, or appendages. At a later stage the vegetative point 

 is found to consist of dcrmatogen, which layer covers a meristematic 

 mass undifferentiated into periblem and plerome. At tbe base of the 

 growing point the first leaves appear in their order. Certain procambial 

 threads reach from the fibrovascular bundle of the sucker to the more 

 developed leaves. The points of growth of tbe roots may be seen in the 

 middle of a mass of cortical tissue, the elements of which are large. 



Young plants of 0. minor differ from G. cruenta in that they are 

 provided with more numerous roots. In 0. Heclerse, on the contrary, 

 the roots are less numerous, and develope more slowly, but the adventitious 

 buds are more numerous. 



M. Hovelacque classifies tbe suckers of Orobanche under four types, 

 viz. : — (1) Small unicellular suckers. When the root of an Orobanche 

 touches the nourishing root of a bost by a very small point, this contact 

 is often limited to a single cell of the superficial layer. The morpho- 

 logical value of these suckers is that of root-hairs. (2) Small multi- 

 cellular suckers. When the contact with the bost affects more than one 

 cell, these cells elongate and penetrate the host in a single mass. (3) 

 Large unramified suckers. When the surface of contact of the parasitic 

 root with the nourishing root is very large, many of the superficial cells 

 take part in the formation of a sucker. In this case the sucker partakes 

 of the character of a very imperfect root. (4) Large ramified suckers. 

 Ramified suckers differ from the preceding only in the fact that, when 

 penetrating the root of tbe bost, they branch. In this last case the 

 suckers of Orobanche are homologous to a bundle of imperfect roots. 



Origin of the Suckers in Phanerogamous Parasites.f — M. Granel 

 states that in Melampyrum pratense the suckers arise in the cortex. The 

 cells of the piliferous layer, after elongation, divide into a filament of 

 cells ; one, two, or three cells from the middle of each filament elongate 

 rapidly towards tbe exterior, and imbed themselves in the host. 



Among plants with temporary suckers, some develope their organs of 

 absorption on their roots ; these are, for example : Osyris alba, Thesium,, 

 Melampyrum, Orobanche minor. In others the suckers arise in tbe 

 stem; for example: the Cuscutese, Cassytha, &c. Osyris alba possesses a 

 large number of normal roots, and also has suckers. It presents then a 

 coexistence of free and parasitic life. In conclusion the author states 

 that in Osyris alba, Orobanche minor, and Thesium divaricafum, the origin 

 of tbe suckers is to a great extent identical; they arise in the cortical 

 parenchyma, and are joined slowly by some cells formed by the pericycle. 



Arrangement of Secondary Roots and Buds on Roots.J — H. P. van 

 TiegLem discusses the laws which govern the arrangement of the lateral 



* Comptes Rendus, cv. (1887) pp. 470-1, 530-3. 

 t Bull. Soc. Bot. France, xxxiv. (1887) pp. 313-20. 

 X Ann. Sci. Nat.— Bot., v. (1887) pp. 130-51. 



