•60 SUMMARY OF CURRENT RESEARCHES RELATING TO 



while the vigour and length of the haulm depend mainly on the amount 

 of water in the soil at the time of germinating. In wheat the length 

 of the ear is also chiefly determined by the amount of water in the soil 

 during the first period of growth. 



Parasitism of Pedicularis.* — According to A. Volkaert, the various 

 species of Pedicularis are parasitic almost exclusively on species of 

 Graniinea3 and Cyperaceae, doing considerable damage in this way to 

 pastures ; P. 2^lustris is in this respect the most injurious species. 

 The haustoria appear, in some species at least, to persist through the 

 winter. Some species choose especially particular grasses for their 

 host-plant ; thus P. recutita is partial to Deschampia csespitosa, P. verti- 

 cillata to Sesleria coerulea. The various species differ greatly in the 

 obligatory character of their parasitism ; thus P. palustris displays the 

 strongest parasitism ; while P. comosa is almost independent of any host- 

 plant. 



Parasitism of Ximenia americana. f — Further experiments by E. 

 Heckel on the germination of the seeds of this plant show that it is a 

 true root-parasite. It produces suckers altogether resembling those of 

 Thesium, which do not fix themselves indifferently to the root of any 

 plant with which they may come into contact, and, in the absence of a 

 suitable host-plant, may become autoparasitic, attaching themselves to 

 another stem or root of the same species. In addition to the suckers, 

 the root of Ximenia normally produces nodosities or tubercles resembling 

 those of the Leguruinosas, which appear to be connected with the nutrition 

 of the plant. 



Germination of some Perennial Herbs.J — A. Eimpach has studied 

 the germination [and development of some perennial herbs of North 

 America, which he classifies under three heads, viz. : — (1) those which 

 possess a rhizome which grows more or less vertically upwards, and 

 becomes drawn down by contractile adventitious roots (Lilium Martagon, 

 Allium ursinum, Plantago major, species of Arissema, Hypoxis, Trillium, 

 &c.) ; (2) the roots have a nutritive function only ; they are of no great 

 importance in fixing the plant to the soil, and produce no contractile 

 rootlets (Paris quadrifolia, Colchicum autumnale, Orchis mascida, species 

 of Erytlironium, Lilium, &c.) ; (3) those which are furnished with a 

 long tap-root, are confined to the place they occupy when germinating, 

 and are reproduced only by seeds (a very common form on the prairies). 



Germination of the Winter-buds of Hydrocharis Morsus-Ranae.§ — 

 According to J. A. Terras, the winter-buds of the frog's-bit separate 

 from the runners as soon as they are ripe, sink to the bottom of the 

 water, where they rest till the following spring, when they rise to 

 the surface and develope at once into new plants. By covering up, 

 tbey may be kept in their resting condition for at least two years. 

 Heat and light by themselves are insufficient to induce germination ; a 

 co-operation of the two is necessary, as also is the presence of oxygen. 



* 'Unters. iib. d. Parasiti6mus d. Pedicularis-ArteD,' Zurich, 1891), 52 pp. See 

 Beih. z. Bot. Ceutralbl., ix. (1900) p. 521. 



t Comptes Rendus, cxxxi. (1900) pp. 7G4-5. Cf. this Journal, 1900, p. 354. 



X Bot. Gazette, xxx. (1900) pp. 171-88. 



§ Trans. Bot. Soc. Edinburgh, xxi. (1900) pp. 318-29. 



