86 SUMMARY OF CURRENT RESEARCHES RELATING TO 



in enormous numbers', 100,000 to 150,000 on an individual, can germi- 

 nate only when in contact with the root of the host ; they may retain 

 their power of germination for two years. The embryo developes into a 

 filiform structure ; and the penetration is effected, as with parasitic 

 fungi, by a secretion from the parasite whieh dissolves the tissues of 

 the host. The young plant penetrates to the vascular bundle of the 

 host, but does not appear to inflict any serious injury upon it. In the 

 endogenous formation of the growing point Orobanche shows a resem- 

 blance to Rafflesia. The structure described by some writers as an 

 " intermediate organ " between host and parasite, results simply from 

 the common growth of the parasite and of the root of the host. From 

 the true haustorium, the portion of the parasite which first penetrates the 

 tissue of the host, secondary haustoria spring, which serve for its non- 

 sexual reproduction. 



With regard to the plants from which the various species of Oro- 

 banche derive their nourishment, this is not altogether indifferent ; each 

 species of parasite has only certain hosts on which it will grow, though 

 these may be numerous and not necessarily nearly related to one 

 another ; thus O. ramosa is parasitic on the hemp and on tobacco. 

 O. minor was found to grow on forty-four different species, O. ramosa 

 on twenty-nine, O. speciosa on thirteen, and O. Hederse on three species 

 of host-plant. 



Biology of the Mistletoe.* — Dr. M. Kronfeld describes at length 

 the mode of life and germination of the mistletoe. He states that 

 the popular idea that the seeds can germinate only after passing 

 through the intestinal canal of a bird, is correct only with considerable 

 limitation. No doubt seeds are occasionally passed with the excreta, 

 and are then in a favourable condition to germinate. But the 

 majority of the seeds are rejected by birds when feeding on the white 

 pulp of the fruit. The seeds can easily be made to germinate in 

 the ordinary way, but require a long period of rest after ripening. The 

 mistletoe is also propagated non-sexually by buds. Polyembryony 

 occurs normally, a very large proportion of the seeds containing two or 

 three embryos. 



The development of the plant varies greatly, according to the tree 

 on which it is parasitic ; and this has been the source of the manufacture 

 of a large number of false species. It will grow on almost any tree 

 except certain conifers. It is least luxuriant on other species of 

 Conifers ; most so on Robinia Pseudacacia. 



Root-symbiosis in the Ericacese.j — Herr B. Frank finds this to be 

 an almost universal phenomenon in the Ericaceae. The roots afflicted in 

 this way are distinguished by their extraordinary tenuity (0 • 07-0 ■ 05 or 

 even ■ 03 mm.), greater length, and sparsity of branching. They usually 

 consist of nothing but a siugle slender fibrovascular bundle and epi- 

 dermis, the root-hairs being altogether suppressed. The epidermis is 

 well developed ; the cell-cavities are large, and completely filled by an 

 irregularly interwoven mass of fungus-hyphae. They are also enveloped 

 in a weft of hyphse, which do not, however, form a closed envelope, but 

 are connected in a variety of ways with the intercellular hyphse. The 



* Biol. Centralbl., vii. (1887) pp. 449-64 (3 figs.). 



t SB. Versanirnl. Deutsch. Naturf. u. Aerztc, Wiesbaden, Sept. 21, 1887. See 

 Bot. Centralbl., xxxii. (1887) p. 57. Cf. this Journal, 1886, p. 113. 



