456 Dr. F. A. Bather— Prof. NatJwrsfs Studies of Fossil Plants. 



There is considerable difference in this respect between different 

 classes of material, and it is not always easy to say beforehand whether 

 the remains of a leaf will yield serviceable preparations of cuticle or 

 not. Leaves with a well-developed cuticle, probably as a rule derived 

 from xerophytes, are generally of a brownish colour, and so elastic 

 that they can be more or less completely freed from the stone. 

 Such leaves are frequently presented by the ginkgophytes and by 

 some conifers, e.g. Thinnfeldia, Ptilozamites, and Lepidopteris. Leaves 

 with a relatively thin cuticle may, however, in certain circumstances 

 have been so preserved that they can be treated in a similar manner, 

 e.g. Dictyozamites, Otozamites, and Pterophylliim. All such leaves 

 yield good and fairly large preparations. On the other hand, leaves 

 that are brittle and exceptionally carbonised fall to powder and yield 

 no preparations of value. Between these extremes are all gradations, 

 and even such leaves as resemble a homogeneous mass of coal may 

 furnish good preparations if only large enough fragments of the leaf 

 can be obtained. All these respond differently to the reagents. While 

 leaves of Dietyozamites are completely bleached by Eau de Javelle in 

 a few hours, others take as many days or weeks, or even a longer 

 period, to become sufficiently transparent. The action of the reagents 

 may, however, be hastened by warming. 



When the leaf has become transparent it still consists of the cuticle 

 of the two sides, and these have to be separated with dissecting 

 needles. If a part of the leaf-margin is preserved, it is advisable to 

 bend the cuticle of the under side round the margin so as to lay it flat 

 alongside the cuticle of the upper side while retaining its connection 

 therewith. Thus comparison of the two sides is facilitated. For 

 mounting preparations of cuticle, glycerine- jelly is better adapted 

 than Canada balsam.^ 



Although the use of the microscopic study of the cuticle has been 

 generally recognised since the publication of Schenk's work, still it 

 has scarcely been taken advantage of to the extent that is desirable. 

 In every case the systematic determination of a leaf should be checked, 

 when possible, bj^ the study of its cuticle, since the outer form is so 

 deceptive that one can rarely depend on it alone. A notable instance 

 of this is furnished by the leaves from Greenland which were regarded 

 as Cycas leaves by Heer and all other botanists, and served as basis 

 for many conclusions of importance to climatology and plant-distribu- 

 tion. Eventually study of the cuticle enabled Professor Nathorst to 

 prove that these leaves did not belong to Cycas, but to a new genus, 

 which he named Pseudocycm from its I'emarkable resemblance to Cycas 

 in outer forra.'^ N"one the less, the examination of the cuticle should 

 always be combined with as complete a studj- as possible of the leaf 

 itself. To make and describe preparations of cuticle is easy enough, 

 but is of small value unless one can give some account of the form 

 and structure of the leaves to which they belong. 



To turn to the Spores. Whereas those of the Palaeozoic Lycopodiales 



' A. G. Nathorst, 1907, " Paliiobotanische Mitteilungen, No. 2, Die Kutikula 

 der Blatter von Dietyozamites Johnstrupi, Nath." : op. cit., xlii, No. 5. 



* A. G. Nathorst, 1907, " Palaobot. Mitt. No. 1, Fseudocyeas, u.s.w.": ibid. 



