40 Proceedings of Indiana Academy of Science 



await solution concerning the trichomes other than root hairs found 

 in plants. 



In Tortula the rhizoidal cross walls are oblique (11, p. 204) when 

 first formed. It is by no means decided that in this plant and in other 

 mosses this oblique position is for the purpose of offering the greatest 

 amount of surface for diosmosis and conduction in the filament. Some 

 roots that normally grow beneath the ground when cultivated in clear 

 water are in certain instances positively heliotropic and in others nega- 

 tively so. This shows an ability to respond to a stimulus and is not 

 inherited by them according to Darwinian principles (14, p. 733). Not- 

 withstanding the admirable researches of Czapek on the corrosive effect 

 of roots, the nature of the various secretions is still undetermined 

 (15, p. 107). 



Such questions as the following have a physiological bearing: juxta- 

 posed or superimposed apical cells; the length of time a procambium 

 cell can produce new elements; the physiological significance of an- 

 thocyanin ; and cuantitative estimation of transpi rational reduction by 

 felted trichomes (11). The irritant of Urtica dioicd formerly thought 

 to be formic acid but now determined to be an albuminoid substance 

 (11) should be studied in other representatives of the genus. Other 

 problems are iridescent plates of the Rhodophyceae, velamen condensa- 

 tion, and the significance of oblique palisade tissue (11) ; and the cul- 

 tivation of various embryos as shown by Hannig (16) and others. 



The old question of the ascent of water is still unanswered not- 

 withstanding all that has been done to solve it. Strasburger studied 

 the problem and arrived at certain valuable conclusions (1, Bd. I, p. 

 207) but was not able to explain the situation and, like the "note- 

 worthy experiments" of Dixon and Joly (17), left the question unde- 

 cided. The theory of Sachs soon became untenable although the force 

 of imbibition is sufficient for the purpose. The great force cf imbibition 

 is shown by the swelling of starch which according to Rodewald requires 

 a pressure of 2,523 atmospheres to prevent it (1, Bd. I, p. 63). In 

 dried seeds imbibition and osmosis work together. This force is some- 

 times made use of to split skulls for anatomical pu.rposes (1, Bd. I, p. 

 63). This force is, however, small in comparison with the freezing- 

 expansion of water at — 20° C. which would require a pressure of 

 13,000 atmospheres to keep ice from forming (1, Bd. I, p. 29). Thus, 

 we have the reason for the formation of frost rifts in the wood of 

 various trees. These rifts are mostly radial and along the lines of 

 least resistance (1, Bd. I, p. 307). The loud pistol-like reports often 

 lieard in living timber during extended and very cold weather indicate 

 the formation of these rifts. The question of pressure affects even the 

 plant when growing for it was first shown by Hales and afterwards by 

 Kraus (1, Bd. I, p. 74) "that tree stems and fruits swell slightly 

 at night and decrease in the day time due to transpiration although 

 such changes in tree trunks are generally less than one per cent." 



Other questions that crowd themselves on our attention are: the 

 pressure necessary to close bordered pits ; the physiological importance of 

 tyloses; certain functions of Icptome parenchyma, especially in relation 



