March 22, 19 17] 



NATURE 



7o 



A GROUP OF FOSSIL PLANTS.^ 

 ^[""HE publication of Mr. Wieland's first volume in 

 •*- 190b was an event of great importance which 

 had a wide inHuence on botanical research. The 

 author gave an account of tne ttoral and vegetative 

 morphology of several species of Cycaaeoidea, a genus 

 represented in Upper Jurassic and Lower Cretaceous 

 strata in many parts of the world, but nowhere on 

 so large a scale as in the Lnited States, where 

 hundreds of well-preserved trunks have been found. 

 Though agreeing generally in habit and in most 

 anatomical features with recent Cycads, Cycadeoidea 

 is characterised by reproductive shoots of a type far 

 removed from that of the existing members of the 

 Cvcadaceae. The work accomplished by European in- 

 vestigators since Wieland's first volume was published 

 is summarised in the present volume, which also con- 

 tains many hew facts and amplifies the earlier de- 

 scriptions ; it also includes some account of the 

 author's Mexican expedition in 1909-10, which yielded 

 a rich harvest of Liassic Cycadean fossils. Incident- 

 allv Mr. Wieland emphasises the importance of per- 

 sonal observation in the field, and gives salutary advice 

 to many of us who have neglected this part of a palaeo- 

 botanist's duties. He directs attention to the short- 

 sighted policy of some museum authorities in refusing 

 to allow their specimens to be disfigured by the lapi- 

 dary's wheel. 



The American Cycads are divided into groups in 

 part geographical and in part morphological, and each 

 set of forms is critically discussed from a taxonomic 

 point of view. The Maryland stems agree closely with 

 the English specimens described by Buckland from 

 Portland, and British students are reminded that they 

 have not fully investigated their own material. Two 

 of the most interesting species described and beautifully 

 illustrated are Cycadeoidea colosallis and C. Dartoni, 

 the latter founded on a portion of a trunk bearing 

 500 to 600 strobili, most of which contain well-preserved 

 seeds and embryos. A chapter on the seeds of Cyca- 

 deoidea is especially interesting ; in it the author 

 develops more fully his views on the evolutionary history 

 of seeds as represented more particularly by those of 

 the Bennettitales. The structure of the American seeds 

 agrees in essentials with that of European t\'pes, the 

 most complete account of which we owe to the late 

 Prof. Lignier. Wieland institutes comparisons be- 

 tween the Mesozoic Cycadean seeds and several Palaeo- 

 zoic genera, such as Lagenostoma, Conostoma, and 

 others, and in the course of the discussion he gives a 

 summary of recent work on the older seeds. He sug- 

 gests that the genus Codonotheca, usually regarded as 

 the male flower of some Pteridosperm, may be a bi- 

 sporangiate shoot, which originally contained a central 

 seed, though there is no definite evidence of this, 

 surrounded by a whorl of microsporophylls. His con- 

 tention is that the complex seed-coats of Palaeozoic 

 and later types are the result of sterilisation and fusion 

 of encircling leaves or sporophylls round a central 

 spore; in other words, he interprets the elaborate seed- 

 coats as reduced foliage-organs which have become 

 intimately associated with a megaspore. It is, how- 

 I ever, noteworthy that the bisporangiate flowers of such 

 a type as Cycadeoidea colosallis are apparently more 

 primitive than the much older Palaeozoic seeds, which 

 I show no trace of any encircling whorl of leafy organs. 

 ' In a chapter on Cycad derivatives Wieland ranges 

 I over a wide field, but without committing himself 

 ; definitely to anv clearly defined view on the question 

 I of a relationship between the Angiosperms and the 

 ■ Cycadean stock. He holds that the columnar, and 

 often unbranched, stems characteristic of the great 



' "American Fo<isil Cycads." Vol. ii., "Taxonomy." By G. R- v\ ielsnd. 

 Pp. r-j67+plate5 i-lviiL (Published by the Carnegie Institution of Wash- 

 ington, 1Q16.) 



NO. 247^, VOL. QqI 



majority of the Cycadeoideas are an unusual type derived 

 from a much more slender and freely branched ances- 

 tral form. Comparisons are made between the Mag- 

 noliaceag and the Bennettitales, and reierence is made 

 to opinions on the evolution of the Conifers, tne posi- 

 tion of the Gnetales, and other questions. His survey 

 of the fossil Cycads leads to the conclusion that the 

 true Cycads were probably never more abundantly re- 

 presented than they are to-day : they were preceded by 

 the Cycadeoidea type, a comparatively stereotyped 

 form, and at an earlier stage the Williamsonia group 

 occupied the dominant position, a group exhibiting a 

 much greater range in the form of flower and stem. 

 Some account is given of Cycadean foliage from 

 Mesozoic strata, and of the rise and decline of the 

 Cycad element in Mesozoic floras from the Rhaetic to 

 the early Cretaceous period, when the Angiosperms 

 assumed the leading role. 



Mr. Wieland's second volume is a contribution of 

 considerable importance by an author who has well 

 earned the right to speak with authority on a subject 

 of exceptional interest ; but after reading the long 

 theoretical discussions, which are suggestive, though 

 the conclusions are often open to question, one regrets 

 that more attention was not paid to the elucidation of 

 several morphological problems that are still unsolved, 

 and on which the splendid American material can 

 undoubtedly throw much light. The author is an 

 enthusiast with a vivid imagination, and does not 

 always fully appreciate the difficulties of the problems 

 before him ; his desire to solve the mysteries of the 

 early stages in plant-evolution leads him into deep 

 waters of speculation, and his points are nol always 

 easy to grasp owing to a diffuse style and the lack of 

 concise summaries of conclusions. The photographic 

 plates are probably the most striking illustrations of 

 fossil plants ever published, and the student owes a 

 debt of gratitude, not only to the author, but also to 

 the officials of the Carnegie Institution. 



* A. C. Seward. 



METEOROLOGY AND THE SOLAR 

 CONSTANT. 



I HE Journal of the Scottish Meteorological Societv 

 * (No. xxxiii.), recently issued, cx)ntains, as usual,, 

 some ver\- interesting articles. 



Lieut. Etouglas, Royal Flying Corps, gives some 

 details of his experience during his ascents amongst 

 the clouds in northern France. He finds stratus cloud 

 most frequently in anticyclones and round their 

 eastern and northern borders. Tlie top in such cases 

 is verv flat and even, and an inversion of temperature 

 is met with at the upper surface. The lowest tem- 

 perature is generallv at the top of the cloud, but is 

 occasionally met with a little lower. If cumuli attain 

 sufficient height they develop into thunderstorms, but 

 at least 6000 ft. from top to bottoin is required for 

 this to happen, and on all occasions in 19 16 when 

 thunder developed, the height was not less than 

 10,000 ft. Mr. Douglas states that cirrus and cirro- 

 stratus almost certainly consist of thin snow. 



Dr. Knott discusses the value of the solar constant 

 and the associated problems, givinf? chiefly a sum- 

 mary of the work of Abbott and Fowle and .Anders 

 .Angstrom. He explains ver\- lucidly the method de- 

 vised by Langley, by which the error caused in deter- 

 mining the oinstant by the selective absorption and 

 radiation of the air is overcome. The values obtained 

 for the constant range from 1-97 at Washington to 

 1-92 at Mount Whitney (14,500 ft.), the mean of 573 

 obsen'ations at Mount Wilson (5670 ft.) gives 1-93, 

 and Dr. Knott c»nsiders that we may take these 

 results as correct, so that the solar constant is very 

 nearlv 2 gram-calories per cm.^ per minute. This is 



