418 THE JOURNAL OF BOTANY 



this are abundant in Lincolnshire, and are not more than eighty 

 or ninety years old. It seems probable that the pistillate form of 

 this tree never attains so great a size, at any rate in this country. 

 In shape the seeds are oblong-oval, the base blunt and porous, 

 and the whole surface minutely tomentose with a few rather 

 longer silky hairs, which apparently serve the purpose of absorbing 

 moisture. In P. canescens the seeds are rounder and much more 

 minute, and in P. nigra they are narrower and less rounded, but 

 all are of the same dull whitish colour, and tomentose. 



Germination is extremely rapid ; after the seed has been freed 

 from the cottony down enveloping it and soaked in water, the 

 radicle appears in one or two days, and in the case of the seeds of 

 P. marilandica from Kew, ten hours in water were sufficient to 

 cause germination. Reference to the accompanying plate will 

 explain the stages of growth from the seed to the young plant, 

 complete figures being given of one species from the " White 

 Poplar group " (P. canescens), and of one from the " Black Poplar 

 group " (P. canadensis). The later stage of P. nigra and P. mari- 

 landica resembles, except in minor particulars, tHat of P. canadensis, 

 and is omitted for want of space. A simple radicle~with a short 

 length of stem first protruded from most of the seeds, although 

 some showed the cotyledons before the root. Those which deve- 

 loped a central root proved afterwards to be the strongest plants. 

 On the second day a circle or fringe of delicate root-fibres appeared 

 around the base of the stem, and when the young plant was 

 placed upon damp sandy soil, these fibres immediately began to 

 attract to themselves particles of sand and earth. In two days 

 the testa was thrown off, and the minute fleshy cotyledons began 

 to spread apart and to show a tinge of green, the stems becom- 

 ing reddish. (For these stages of growth see figs, lb, 2b, 3 a, 

 and 4 a.) 



After five or six days the cotyledons were well developed, 

 flattened out laterally, and bright green. In shape they were 

 orbicular, sagittate at the base, thick and succulent, glabrous, 

 pale yellow at first, then bright green without the tinge of red so 

 noticeable later in the leaves and stems. The central bud then 

 grew rapidly, and in three weeks the first pair of leaves were half- 

 an-inch long. Those of P. canadensis, P.jiigra, and P.jmari- 

 landica were linear-oblong, ^toothed at the margin — the* teeth 

 placed at a much greater distance apart than in the second and 

 third pairs of leaves later developed — the horny incurved tip of 

 each tooth so remarkable in full-grown leaves of these species 

 being distinctly visible, and the whole plant glabrous. In later 

 stages of growth these characteristics were maintained, but the 

 upper leaves of all species gradually became broader, although 



they were far from resembling in shape those of a full-grown 

 tree. 



Later growth and development were less rapid, for, about four 

 months after germination, the largest of the young plants (P. 

 canadensis) were only two inches high, although in a flourishing 

 condition, and with three pairs of leaves about one and a quarter 



