670 EEPORT — 1891. 



for 24-30 hours, and under sucli conditions a marked change in the tissues was 

 visible. The cells of the cortex on the upper side became densely filled with pro- 

 toplasm, while the lower cortical cells were relatively poor in protoplasmic contents. 

 The same changes in the membranes occur as those noticed in Phycomyces, that is 

 to say, the walls of the cortex on the upper side are very much thicker than those 

 on the lower side.' 



Since the walls of the cortical cells have become more resisting on tbe upper 

 than on the lower side, then (assuming the osmotic expanding force to be the same 

 in both cases) the growth will be quicker on the lower side, and the shoot will 

 curve upwards. Wortmann states that bis observations account for the fact that 

 the convex side grows quicker, not merely than the concave, but than a normal 

 unbent shoot. But he does not seem to have compared the thickness of the convex 

 cell-walls with the normal, although he states that they are poorer in protoplasm 

 than is usual, and from this it may, according to his views, be perhaps assumed 

 that the membranes are abnormally thin. 



Wortmann points out that his views account for two well-known features in 

 growth curvatures, viz., the latent period and the after-effect. If a curvature can 

 only occur when a difi'erence in structure of cell-walls has arisen, it is certainly 

 natural that some time should occur before the curvature is apparent. I do not 

 lay much stress on this part of the subject, as I feel sure the whole question of 

 latent period needs further investigation. "With regard to after-eilect it is true 

 that AVortmaim's views account for the continuance of curvature after the stimulus 

 has ceased to act. 



Wortmann attaches great importance to another point in his theory, which, 

 could it be established, would be of the greatest interest, and would unite under a 

 common point of view, not only acellular and multicellular organs, but also naked 

 protoplasm, e.g. the plasmodia of myxomycetes. The view in question was tenta- 

 tively suggested by 8ach?,- and mentioned by Pfefl'er ^ in a similar spirit. The 

 apogeotropic curvature of a phycomyces-hypha is supposed to be due to the 

 unequal thickening of the membrane on the upper and lower sides, and this to 

 be due to tlie migration of protoplasm from the lower to the upper side of the 

 cell. In the same way in a multicellular organ the protoplasm is supposed to 

 migrate from the lower cortex and ])ith to the upper cortex and pith, such 

 migration being rendered possible by the now generally admitted intercellular 

 protoplasmic communication. Thus the apogeotropism of a cell or a multicellular 

 part would be due to the apogeotropism or tendency to migrate vertically upwards 

 of the protoplasm. There are great difficulties in the way of accepting this 

 attractive theor)-. 



Noll ■* states that when a curved phycomyces-hypha, in which protoplasm has 

 accumidated in the upper (concave) side, is reversed so that the mass of protoplasm 

 is below, it does not migrate upward again, as might be expected. Moreover he 

 points out that in Nitella and in Bryopsis the circulating protoplasm continues in 

 movement, and does not accumulate in any part of the cell. Lastly, there seems, 

 as Noll points out, a difficulty in believing in the migration of protoplasm through 

 the very minute pores by which the plasmic strands pass from cell to cell. There 

 seems much probability in Noll's view that the plasmic strands only serve for the 

 passage of impulses, or molecular changes, and that they consist of ectoplasm alone, 

 not of the endoplasm which Wortmann describes as the migratory constituent of 

 the cell. 



Wortmann's theory has been criticised by Elfving.'' The essence of Elfving's 

 paper is that appearances similar to those described by Wortmann can be produced 

 by curvatures not due to stimulation. Thus, when I'hycomyces is made to grow 

 against a glass plate it is mechanically forced to bend. Yet here, where there is 

 no question of stimulation, the plasma collects along the concave side of the ceU. 



' Both protoplasmic change and thickening of cell-walls occur to some extent in 

 the pith. 



^ LehrhiicJi, 1874 ; English tr. 1882, p. 841. 



• PJlan:enphyriologie, ii. p. 331. * Sachs' Arheiten, 1888, p. 530. 



» Finslia Vet. Soc. Forhand. (Helsingfors), Bd. 30, 1888. 



