936 



SCIENCE. 



[N. S. Vol. V. No. 129. 



the plant side, I believe it may fairly be as- 

 serted that the botanist is more favorably 

 provided with subject-matter for investiga^ 

 tion than is the zoologist. For thousands of 

 years plants have been grown, selected and 

 disseminated by man, and have thus be- 

 come his companions, in as true a sense as 

 have the cat, the dog or the horse. For at 

 least a century botanic gardens have ex- 

 isted in all the leading cities of the Old 

 World, for the avowed purpose of promot- 

 ing scientific information along all lines of 

 plant life. For a couple of centuries or 

 thereby the desire to supply novelties of a 

 useful or decorative kind has stimulated 

 the nurseryman to practice artificial selec- 

 tion, which is just Nature's method at work 

 under high pressure and in the hands of an 

 intelligent conductor. Finally, the botan- 

 ist, when he pursues his studies afield, deals 

 with organisms that are rooted in definite 

 areas amid definite environments, and from 

 which slow escape by seeding is alone 

 possible. 



The present-day student of plant biology 

 thus has four rich sources from which to 

 draw information for the discussion of such 

 topics as that now before us. Unfortunately 

 much valuable knowledge that might have 

 been gleaned is lost to us, since its possible 

 practical application in the future was not 

 recognized in the past. Now the botanist, 

 the horticulturist and the agriculturist are 

 joining hands in an efi'ort to gather, to 

 preserve, and to utilize their stores of in- 

 formation. 



Reviewing in thought his different collect- 

 ing fields, every botanist must be impressed 

 by the fact that certain types of plant are 

 broadly associated with certain surround- 

 ings, and particularly is this true of herb- 

 aceous plants. 



If he attempts to sort out these groups in 

 his mind he will refer most of them to one 

 of the following categories : ( 1 ) aquatics, 

 (2) shore or littoral plants, (3) sand or 



xerophilous plants, (4) shade and humus 

 plants, (5) alpine plants, (6) saprophytic 

 and parasitic plants. Not merely could 

 certain broad principles be laid down for 

 each of these divisions ; microscopic study 

 would reveal that in minute details striking 

 similarities reveal themselves in the mem- 

 bers of each group. In what follows I do 

 not propose to adhere to the above group- 

 ings, but will do so where advisable. 



(1) Aquatic and amphibious plants. The 

 Buttercup genus (Ranunculus) includes about 

 469 species, some of which are world-wide 

 in distribution. Nearly all are inhabitants 

 of dry or moist soil, but a few like R. aqua- 

 tilis and R. circinatus are more or less aquatic. 

 In Europe the former exhibits striking 

 diversity, or heterophylly in the leafage, 

 that is largely determined by the relative 

 depth of water and strength of water cur- 

 rent. When growing in ponds or slug- 

 gish streams the submerged leaves are dark 

 green, fiaccid usually, dissected, and devoid 

 of stomata, but at the ends of the annual 

 shoots and just below the flowers are several 

 floating leaves with expanded, trilobed, 

 light green lamina, that greatly resemble 

 the basal leaves of many land buttercups. 

 Stomata are present over their upper sur- 

 faces. In Eastern America the form with 

 submerged leaves alone exists, and even 

 where the plants may be semiterrestrial or 

 completely so, as in the variety caspitosus, the 

 lobed leaves of the European variety do not 

 develop. Such facts cause us to ponder the 

 questions of adaptability and inhei'itance, 

 but do not in themselves lead us far in our 

 present inquiry. 



The Bistort genus (Polygonum') is typically 

 a terrestrial one, but includes one species, 

 P. amphibium, of highly plastic build. When 

 growing in rather deep water it forms flac- 

 cid leaves on long leaf-stalks, and these 

 spring from beside glabrous stipules. On 

 dry land firm leaves with short stalks and 

 hispid stipules appear. These constitute 



