June 18, 1897.] 



SCIENCE. 



939 



4Bhortened, its cuticle thickened, its cells 

 filled with mucilage, its short swollen 

 branches covered with spines, and its now 

 small, succulent, centric leaves short-lived 

 to the extent of a month or six weeks as a 

 gradually perfected resistance to opposing 

 agents. Goebel's experimental results* 

 with the Cacti prove that removal of them 

 to shade and moisture will materially affect 

 their habit. 



(4) Prostrate plants. In my paper on 'The 

 sensitive movements of some flowering 

 plants under colored screens,'! I de- 

 scribed the variations constantly noted in 

 Cassia niditans when grown in the shade on 

 rather moist loam, or in the open on some- 

 what retentive soil, or when fully exposed 

 to the sun and grown in dry sand. Strik- 

 ing microscopic differences characterize 

 each. This plant is but one of many that 

 show like variations, and not a few of them 

 can be studied as one passes along the 

 quieter streets of our cities. The somewhat 

 loose open growth, ascending branches and 

 spreading leaves of Euphorbia mamdata when 

 it springs up in a moist shady place differs 

 from those of the humifuse plant with 

 flattly applied leaves that springs up be- 

 tween the bricks of our neglected side 

 walks. Curiously enough, when the latter 

 is attacked by a Uromyces the habit of the 

 shade grown plant is assumed. Several 

 grasses, Portulaca oleracea and Mollugo verti- 

 cillata are all common humifuse plants when 

 ' baked ' in dry places. 



(5) Alpine plants. Every botanist who 

 has observantly climbed some mountain 

 that rises abruptly from the sea front to an 

 elevation of 3,000-4,000 feet must have 

 been impressed with the change assumed 

 by the vegetation as each successive 1,000 

 feet is surmounted. On the higher exposed 

 elevations dense, tufted, adpressed plants 

 with short flowering stems and white or 



* Flora, 1895. 



fBot. Central., Vol. 61, 1895. 



bright colored flowers are encountered. 

 These often exhibit close afi&nity with low- 

 land species of more luxuriant growth and 

 delicate foliage. Are these Alpines then, or 

 the lowland ones, a product of their environ- 

 ment ? For the present purpose it will suf- 

 fice if evidence can be adduced to prove 

 variation transitions from one to the other. 

 Thanks to the beautiful researches of Gas- 

 ton Bonnier,* supplemented by those of Du- 

 four,t Lazniewski,J Leist,§ Wagner || and 

 Wiesner,^ we can trace surprising varia- 

 tions within a short period of growth. 



Bonnier divided certain plants into three 

 or more parts ; he placed one in alcohol, 

 another in a lowland situation, and the re- 

 mainder on an alpine height. The marvel- 

 ous transformations wrought in the last are 

 described in the text and faithfully repro- 

 duced in his plates. I will content myself 

 with his conclusions. The rhizomes or 

 other underground parts, become length- 

 ened in order the better to store reserve- 

 material, since the aerial period of vegeta- 

 tion is short but intense. The aerial inter- 

 nodes become greatly reduced ; the leaves 

 become smaller but considerably thicker ; 

 those species that have scattered hairs on 

 low ground have them increased in size ; the 

 flowers are reduced in size but brightened 

 in their red and purple colors. Equally 

 marked are the histological changes. 

 Here we have explained the origin of 

 those specific varieties now designated 

 nana, alpina, etc., which reproduce them- 

 selves by seed amid their natural surround- 

 ings. How far a plant or group of them 

 when isolated will remain ' true,' or revert, 

 or vary further, we have as yet no experi- 

 mental data for determining. This much 



* Ann. des Sc. Nat. 7th Ser., Vol. 20. 



t Ann. des Sc. Nat. 7th Ser., Vol. 5, 1895. 



t Flora, 1896. 



? Mittheil. der Natarforsch Geaell. von Bern, 1889. 



II Sltz. der Kais. Akad. der Wisa. in "Wien, Vol. 2, 

 1892. 



T[Ber. der Deutsch. Bot. Gesell., Vol. 9, 1891. 



