Problems of Plant Physiology 49 



of plants to heat require study. Pouchet found that the seeds of Medicago 

 would germinate after boiling in water for four hours (1, Bd. II, p. 

 294) while the seeds, from stone fruits that have been made into jam, 

 germinated (9, Vol. II, p. 230). The subject of desiccation leaves numer- 

 ous questions to be settled. Much attention has been given to a study 

 of the effect of freezing on plants but still it is not known why freezing 

 kills some plants and does not affect others. The resistance of bacteria 

 to freezing requires further explanation (1, Bd. II, p. 314). The 

 resistance of trees which form oil in cold weather as well as the ability 

 of the same plants to withstand cold at different stages of their develop- 

 ment needs solution (1, Bd. II, p. 317). A single reference to the work 

 of Miiller-Thurgau, Molisch, Goppert, Winkler and Kylin must suffice 

 here. This topic forms a subject of great interest and its value can 

 hardly be over-estimated. Even in reasonably cool situations plants 

 may sometimes be injured by drops of water which concentrate the 

 sun's rays. The resistance of certain marine algae which grow at -1.8° 

 C. requires attention, as does the statement that the spores and mycelia 

 of Mucor are equally resistant, and whether or not ice forms in turgid 

 bacterium cells (1, Bd. II, p. 310). 



Dry spores such as those of Aspergillus and yeast are only slightly 

 or not at all injured by submergence in absolute alcohol, ether, benzol 

 or carbon dioxide. The point now arises how they would com^jare with 

 spores in air (1, Bd. II, p. 324). Do roots of seedlings require gradual 

 moistening to recover and live after drying (1, Bd. II, p. 324) ? A 

 further comparative study of the spores of bacteria and seeds would 

 net additional worthy results. Notwithstanding what has been done 

 on the effect of different alkaloids and on the various poisonous plant 

 substances, there remain many problems for investigation by the physi- 

 ologist. 



Certain questions concerning the germination of seeds and the sub- 

 sequent transfer of materials require investigation. There are questions 

 of cortical and medullar functions which need attention. Schimper 

 (72) has shown that the bundle sheaths in Plantago could convey sub- 

 stances, but less rapidly, after the removal of the fibro vascular bundles. 

 In young tissues the Biuret reaction is useful in showing the disappear- 

 ance of certain substances, as soluble proteids. Companion cells need 

 study and the questions concerning latex are by no means settled. The 

 writer by depriving the seedlings of Papaver of their latex checked the 

 growth but did not kill the seedlings. The same experiment the author 

 has performed on certain sieve tubes with similar results. Schwen- 

 dener states that no latex escapes from withered plants or old parts 

 when cut (1, Bd. I, p. 594). 



If nine tenths of all phanerogamic seeds possess oil, as Nageli states, 

 it can be seen that this does not necessarily protect them from desicca- 

 tion. (1, Bd. I, p. 609.) Puriewitsch and others planted grains of 

 certain plants from which the embryo had been removed and the 

 endosperm was neither changed to sugar nor removed. When, however, 

 the place of the embryo was taken by substituting a small cylinder of 

 gypsum whose lower end reached into water, to remove the forming 



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