176 



of the individual cells, due to the turgor produced by the water from the 

 roots, and the conclusion is at once reached, that a scanty supply of water 

 during the time of growth must produce small dwarf specimens. ICach 

 excursion through sandy regions, in which a damp subsoil is cither lacking 

 or lies very deep, furnishes examples enough for this fact. I have published 

 detailed measurements concerning the shortening of cells due to a scarcity 

 of water'. Moller- furnished experimental proof of dwarfing due to scar- 

 city of other food substances with an excess of water and also confirms the 

 principle that in slightly concentrated nutrient solutions the root increases 

 relatively in size. Mobius'' has arrived at the same result in his comparative 

 cultures with Xanthium in sand and loamy soil. He found the roots and 

 stalks of plants grown in sand branched more than those of plants grown in 

 loamy soil, while the leaves were more slender and the glandular hairs 

 fewer in number. On the other hand, in plants grown on loam the content 

 of calcium oxalate cr}'stals seemed smaller. The thorns were smaller on 

 sandy soil, but the walls of the lignified cells seemed considerably thicker. 



Comparative studies of the influence of dr)- or wet localities were made 

 by Duval-Jouve'. These proved that in dry, hot i)laces, a formation of the 

 hard, bast bundles is especially favored, but is retarded in shady, wet posi- 

 tions. Volken's observations'' on Polygonum amphih'mm in the forms grown 

 in sand, heath and water, are very thorough. In the sand form the circum- 

 ference of the stem is smaller, at the expense of the central air canal; the 

 bark cells are more heavily thickened, while between the bark and the 

 phloem, a rather broad ring of uncommonly thick mechanical cells is en- 

 closed. A closed wood cylinder is formed, the vascular system in which is 

 almost 2 to 3 times as strongly developed as in the water-grown stem ; in 

 the latter, the absence of thick-walled elements and the occurrence of large 

 air holes facilitate floating. The petioles of the water form, which have no 

 mechanical reinforcement, may become six times as long as in the land form, 

 the midribs of which are strengthened by strong collenchyma cords. The 

 palisade cells arc more strongly developed in tlie water plants, but these 

 lack, on the other hand, the strongly developed bristles on the upper sur- 

 face and here also the somewhat larger epidermal cells which in the land 

 form contain a slimy content, explained by Volkens as a water reservoir in 

 times of great drought. In the well-known Rose of Jericho (Anastatica 

 hierochuntica), that plant of the desert which closes together like a head 

 when dry, the inclination of the branches toward each other arises from the 

 fact that the wood cells on the different sides of each branch possess a 

 different capacity f(jr swelling longitudinally, which goes hand in hand with 

 an unequal lignification. 



1 Sorauer, Bot. Zeit. 1873. 



- IM(illcr, Beitrage zur Kenntnis d. Verzwergung. T^andw. Jahrb. 1893, p. 167. 



• iMii))ius, M., Ueber den Kinfluss des Uodens auf die Struktur von Xanthium 

 spinosum usw. Ber. d. Deutsoli. Bot. Ges. 1905, Vol. XXII, Part 10. 



^ Duval-Jouve, Anordnung der Gewebe im Blattc der Griiser. Bot. Jahresb. v. 

 Just 1875, p. 432. 



•'■> Volkens, Beziehungen zwischen Standort und anatomlschem Bau der Vegeta- 

 tionsorgane. .Tahrb. d. Kgl. Bot. Gartens zu Berlin. Vol. Ill, 1S84, p. 46; cit. Bot. 

 Centralbl. 1884, No. 46. 



