Problems of Plant Physiology 43 



of our vessels that move on water. The recent valuable list of papers 

 by Haberlandt on "The Physiology of Cell-Division" deserves considera- 

 tion in this connection. 



Overton (28) presented a rather plausible theory concerning the 

 permeability of the protoplasmic membrane which was afterwards sup- 

 posedly confirmed (29). Later studies, however, have thrown a cloud 

 of uncertainty over his rather ingenious theory and further study of 

 this important subject is necessary. The question of the penetration 

 of aniline dyes into the living protoplasm was worked out by Pfeffer 

 (30). The exact way in which an accumulation of dye occurs in cer- 

 tain plants remains to be explained. 



Pfeffer's (30, Bd. I and II) woi-k on chemotaxis is also of far-reach- 

 ing importance. From the osmotactic standpoint the question arises 

 concerning a tactic or phobic response in strong solutions. Sperma- 

 tozoids and bacteria (1, Bd. II, p. 813) were caused to enter a capillary 

 tube containing only .00000001 milligram of malic acid or peptone. 

 Relatively, these amounts are not so small as they would seem since the 

 speiTus weigh only about .00000025 milligram and a cell of "Bacterium 

 fermo" about .000000002 milligram. On the other hand stronger solu- 

 tions having an osmotic value of 0.5 per cent KNO; produce negative 

 osmotaxis (1, Bd. II, p. 813). Englemann has introduced an excellent 

 method of demonstrating chemotaxis in which certain organisms such 

 as "Bacterium termo," Spirillum undiila and Spirilluvi tenue are used. 

 By his delicate test .000000001 milligram of oxygen can be detected 

 (1, Bd. I, p. 292). 



In the various processes of growth interest attaches in many ways. 

 The position of the nucleus in growing parts such as root hairs may 

 not always be in the most active part of the cell as the writer has 

 shown. The rapid gi'owth of certain plants or plant parts is well known. 

 It is estimated that "a bacterium can under favorable conditions divide 

 in 20 to 30 minutes. At this rate in three days 4,772 trillions of in- 

 dividuals would be produced." 



Can all plants live when continuously illuminated? Plants in the 

 polar regions do this and McKinney has shov\m that a certain amount 

 of continued illumination is without effect (31, p. 222). 



Growth may be checked locally by cold and still continue at other 

 points. This was well shown by introducing the top of a defoliated 

 clematis plant into a hothouse. Leaves were formed on the stem in the 

 greenhouse while the part outside was still frozen and dormant (32). 

 This development of transpiring leaves proved that in spite of the low 

 temperature outside a large amount of water was absorbed by the roots 

 from the frozen soil and carried through the stem. Knight long ago 

 demonstrated that a plant exposed to transitory cold sprouted earlier 

 than those maintained continuously in a greenhouse. The same phe- 

 nomenon was observed by Pfeffer in various plants and by Miiller- 

 Thurgau in potato tubers (1, Bd. II, p. 266). Molisch reports that 

 potato tubers placed at once in an ice box for 14 days at +1 to 3°C will 

 grow at once if planted in a warm house. In case of an early variety 

 one may thus obtain two crops in the same year (33, p. 272). Plants 



