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their habit being so différent from that of the Pteridophyta 

 and more resembling some of the Phaeophyceae, lead to 

 the supposition that the views held by Dawson were 

 erroneous and that Psilophyton belonged to the Sea-weeds. 

 This view has lately been supported by Pohlig (1916, 

 p. 225). 



Some years ago, in the middle Devonian of Rhynie, 

 Àberdeenshire, in Scotland, plant-remains were found, 

 petrified by impetration with silicous matter, which showed 

 many structural détails. Thèse petrefacts hâve been studied 

 by Kidston and Lan g, (1917 — 1921) whose investigations 

 threw light on many interesting points. The chief resuit 

 of their researches was the establishment of the fact, that 

 thèse are the oldest land-plants known, and in many respects 

 of a very simple structure. 



The most typical form of this flora is the genus Rhynia, 

 of which 2 species hâve been distinguished ; their stems 

 are rounded, slender, provided with protubérances and 

 dichotomously forked ; the sporangia are placed at the 

 top of the branches. The stems possessed a central vascular 

 bundle consisting of annular tracheides, surrounded by 

 thinwalled tissue and a clearly defined cortex. The epi- 

 dermis is provided with stomata. Thèse features demonstrate 

 the great resemblance between Rhynia and Psilophyton, 

 on which the authors (1917, p. 776) and E. À. N.Arber 

 (1921) has laid much stress. 



The study of this resemblance is of a great importance; 

 if they are identical, it will be possible to clear up some 

 détails, not only as regards their morphological features, 

 but also as to their condition of life. This is important for 

 judging whether a number of characteristics, which might 

 be considered as primitive, are really so, or may be con- 

 sidered as adaptations to their mode of growth. For this 

 reason I hâve investigated some Psilophyton material ; 

 I had also at my disposai some thin sections of Rhynia. 



