OEEGAEIOTrSNESS AND SOCIABILITT Or BPBCIKS. 97 



youth by the dense and stronger roots of other species, even of the 

 grasses. 



(<) Its winged seed, which in spite of its size and great weight, 

 is often wafted away more than 50 yards from the parent tree. 



(m) Its great resistance to frost, except in damp low localities. 



Sissu. 



This tree, as a gregarious species, is confined to the rumerous 

 flat expanses of loose silty deposits left by the flood-waters of 

 Himalayan streams, where, after debouching into the plains, they 

 spread out over a great width, often branching into a number of 

 shallow arms, which embrace between them islands of various sizes. 

 The loose open soil, from being for a time under water, occasionally 

 dries down to a depth of as much as twenty feet, if not more. The 

 gregariousness of the species is, of course, due chiefly to the pecu- 

 liar nature of the soil and situation which it afi^ects ; but a number 

 of other causes also contribute in their respective degrees to the 

 same end. The more effective of the various causes may be thus 

 summarized : — 



(a) The exclusive character of the soil and locality in which 

 alone the sissu can come up, only khair, Zizyphus and a few other 

 species being able to grow there in appreciable numbers. 



(&) Its ability to stand extreme temperatures, especially frost, 

 which is ob-sdously very severe in the low and, during the cold wea- 

 tlier, moist situations where it grows. 



(c) Its profuse annual, rarely biennial seedinf, and the dissemi- 

 nation in immense quantities of its seed by water in the flooded 

 lands in which it comes up. 



{d) The quick and easy germination of its seeds, especially ua- 

 der the circumstances in which their dissemination is effected. 



{e) The number and great vigour of the coUum-buds in the 

 youngest seedlings, which enables these to continue establishing 

 themselves in spite of violent floods, erosion, deposit of new silt, &c. 

 {f) Its germination only in loose, freshly-deposited silt, in 

 which the young seedliags, owing to their prior appearance, have 

 not to contend with the roots of other species, especially of the. 

 grasses. 



{g) The absence of fires in such places during the time the 

 plants are establishing themselves, there being hardly any grasa 

 present to burn. 



(/(.) The great kngt'i of the trproot of its seedling, and the 

 great depth to which its roots can penetrate. 



