ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 727 



symmetry and by atrophy of the anterior portions, while Tubicaulis is 

 derived from Gyropteris by accentuation of the characters of the latter 

 genus. It is also possible that Anachopterideae may have been derived 

 from the Zygopterideae by loss of the accessory plan of symmetry, such 

 a view being favoured by the characters of the Glepsydropsis series, and 

 this will account for a certain resemblance between Tubicaulis and 

 A nachoropteris. 



Conditions affecting Prothalli of Polypodiaceae.* — G. Perrin has 

 investigated the external conditions which affect the development and 

 sexuality of the prothalli of the Polypodiaceae. Unisexuality is more 

 common than is generally admitted. The antheridia appear early at 

 the base and spread upwards in the lower half. The archegonia appear 

 later upon the median cushion and spread gradually towards the upper 

 notch. They vary from one to eighteen. ' Unisexual prothallia are 

 abundant in certain species of Adiantvm, Aspidium falcatum, and Pteris 

 cretica, but they are generally male. The attempt, carefully made, to 

 connect variations in size or shape of spores with these differences in the 

 sexuality of the prothallia failed. It is in external conditions that the 

 cause must be sought. The principal agents appear to be — (1) nutritive 

 medium ; (2) light ; (3) temperature ; (4) moisture ; (5) time of sowing. 

 A poor medium dwarfs the prothallus and prevents it from producing 

 archegonia. A medium rich in nitrates favours the production of 

 hermaphrodite prothalli. Weak light also has the latter effect, while 

 strong light induces male prothalli. Red light induces exuberant vege- 

 tation and a tendency to unisexuality. The optimum temperature for 

 development is about 25° C. Moisture is indispensable. The time of 

 sowing is important ; the best cultures arise from spring sowing. 

 Summer and autumn sowings induce unisexuality. 



North American Ferns. — W. N. Clutef discusses the question of 

 change of function in dimorphic fronds, namely the appearance of sterile 

 pinnae on the fertile frond, and vice versa, as in Botrychium virginianum. 

 He reproduces! C. E. Bessey's classification of the families of ferns and 

 fern-like plants, both living and fossil. He gives a brief account § of 

 Cystiipteri* fragilis, and describes a new variety, tenuifolia. Having 

 completed his check-fist of North American fernworts with some supple- 

 mentary additions, he gives a summary || showing a total of 304 ferns 

 and fern-allies, and 214 forms. F. C. Greene If supplies some notes on 

 the ferns of Bloomington, Indiana, indicating the habitats of 25 species. 

 A. A. Eaton and W. N. Clute** discuss a question of nomenclature 

 which is provided for in Article 49 of the Vienna Code, namely, whether 

 a varietal name should be retained for a plant when raised to specific 

 rank. A. E. Scoullarft gives briefly the results of her observations of 

 the fruiting of Botrychium in Maine. Having carefully marked robust 

 plants of B. matr&aruyfolium, B. obliquum, and /I. obliquum var. dissectum, 

 she observed them during four summers (1904-7), and found the first 



* Comptes Rendus, cxlvii. (1908) pp. 433-5. 

 t Fern Bulletin, xvi. (1908) pp. 65-8 (1 pi. and 1 fig.). 

 X Tom. cit., pp. 70 4. § Tom. cit., pp. 75 7. 



|| Tom. cit., pp 81-4. f Tom. cit., pp. 68-9. 



** Tom. cit., pp. 77-81. tt Tom. cit., pp. 84-5. 



