BOTANY i 43 



or reduction division similar to the first one which occurs in ordinary meiosis. Further 

 observations by others have, however, not confirmed the latter view. 



A considerable literature has appeared in connection with the enigmatical bodies 

 known variously as chondriosomes, nutochondria and chromidia. Probably a number 

 of different substances have been confused, and whilst the chromidia proper appear to 

 represent true nuclear constituents scattered in the cytoplasm, the significance of the 

 rest is as obscure as their origin is uncertain. 



See L. Digby, "The Cytology of Primula Kewensis" (full citation of literature), An. of Bot. 

 26 (1912); B. Nemec, Das Problem der Befruchtungs vorgange v. andere zytologische Fragen, 

 Berlin, 1910; H. Kemp, "On the Question of the Occurrence of ' Heterotypical Reduction' 

 in Somatic Cells," Annals of Botany, vol. 24 (1910) El. & Em. Marchal, Aposporie et sexualite 

 chez les mousses, Bull. Acad. Roy. Belgique (1911); E. W. Schmidt, Pflanzhche Nutochondrien 

 Progressus rei botanicae, iv (1912); E. B. Wilson, papers in the journal of Exp. Zool., Balti- 

 more, from 1905 onwards. 



Physiology. Considerable advances have been made in our knowledge of protoplasm 

 in relation to its permeability to substances in solution. Czapek especially has devised 

 ingenious experiments which indicate that surface tension plays an important part in 

 permitting or restraining the passage of solutes through plasmatic membranes. He 

 finds that the semipermeability of protoplasm is one of the results of its surface tension 

 properties, and has succeeded in showing that its value, as compared with the surface 

 tension of water, is 0.68. Any substance, in a concentration sufficient to lower the sur- 

 face tension of the water in which it is dissolved to 0.68 will abolish the semipermeability 

 of the protoplasm, and its contents will consequently stream out into the surrounding 

 watery medium in question. There are strong grounds for supposing that the low sur- 

 face tension of protoplasm is to be attributed to the presence of fatty bodies in a state of 

 emulsion, these being necessarily distributed in the surface film, though not of them- 

 selves constituting the whole film in the sense of forming a fatty pellicle such as some 

 have assumed to be present. This view renders it possible to account for the passage 

 of salts in solution into the cell, a point which presented difficulties under the older lip- 

 oid theory of Overton, whilst it is in harmony with the fact that narcosis is produced, 

 with great quantitative exactitude, by substances which dissolve the fatty constituents 

 of the film. Exosmosis then is a physical consequence of immersion in any liquid the 

 surface tension of which is 0.68 or less, but it may also be produced chemically by other 

 substances, irrespective of their surface tension attributes, if they are able to attack and 

 destroy the physical character of the protoplasm by combining with any of its constit- 

 uent substances. Thus a poison may destroy life either by removing the conditions 

 under which the contents of the protoplasm can be retained within the cell, or by de- 

 stroying the organisation of the essential substance of which the cell consists, i.e. the pro- 

 toplasm itself. Other important investigations bearing on the semipermeability of 

 protoplasm and its abrogation have been conducted by Lepeschkin, and the results ar- 

 rived at, though differing in detail, are not very dissimilar to Czapek's. Lepeschkin is 

 inclined to agree with Overton in attributing to lecithin the role played by the lipoid, 

 whilst Czapek regards a neutral fat (which irrespective of the amount present has the 

 surface tension of 0.68) as being the substance more probably concerned. However 

 this may be the recognition of the importance of surface tension in the whole matter 

 certainly constitutes one of the most important advances made in our knowledge of 

 protoplasm within recent times. Not only is it susceptible of quantitative analysis, but 

 the suggestive speculations and researches which it opens up can be similarly checked 

 and controlled. f-^-. 



Observations made in connection with root pressure and kindred phenomena appear 

 to indicate the existence of a difference between the plasmatic membrane on the -side of 

 entry and of exit of a cell as regards its fluid sap. This especially affects the : cells abut- 

 ting upon the vessels and trachaeids of the primary wood of the young root. Lepeschkin 

 in 1906 brought forward strong grounds for believing that a difference of this kind was 

 accountable for the excretion of water from the surface of the sporangiophore of Pilo- 

 bolus, one of the mucorine fungi. It appears difficult to resist the conclusion that a 



