13 



element in classifying ferns. Mainly free-veined ferns occur in 

 Devonian and Carboniferous remains. Anastomosing veins seem 

 to have developed later ; and even now, they form the predomi- 

 nant feature in but two of the ferns of our northern states, 

 Onoclea scnsibilis and Woodzvardia arcolata. The pinnate and 

 fiabellate types of venation are very distinct, but are connected in 

 appearance by a modification of the last type with successive 

 alternations of its dichotomy forming a prolonged axis. The 

 ferns known as gold and silver ferns were included in 1811 in 

 the genus Gywuogramme. Some twenty genera have since been 

 segregated from it, some of them on sufficient grounds. Many 

 garden hybrids and horticultural varieties have been developed. 

 With the exception of a species in Madagascar, the group is 

 confined to the tropics of America, where the species known as 

 the silver fern is perhaps the most common fern known. The 

 goldenback fern of California is perhaps most familiar to ordinary 

 knowledge ; its range is from Alaska to Lower California, but not 

 eastward of the Sierras. In life it is of a bright golden-yellow 

 beneath (often replaced by silvery powder), a brilliant green above ; 

 in the dry season it coils up involutely, exposing only the under 

 surface, which is covered by its peculiar golden waxy powder. 



This and other ferns of the arid region prevent too great trans- 

 piration of water by developing waxy or resinous powders, or by 

 layers of wool or of scales. A Mexican species, Notliolaena 

 aurantiaca, was exhibited, which combines two protections, 

 powder and scales. The silver fern of our arid Southwest 

 finally becomes almost chalky beneath ; it becomes coiled almost 

 into a ball in the dry season. 



Discussion followed upon the true interpretation of the function 

 of the waxy powder, Dr. C. C. Curtis deeming it to accomplish 

 two purposes, that of plugging stomata and that of reflecting 

 heat. Dr. Rusby recalled the suggestion made by Mr. Charles 

 F. Cox some years ago, to the effect that plant hairs carry on 

 metabolism and aid nutrition. 



Dr. Rusby also described the appearance and habitats of several 

 species which he had been familiar with in Bolivia and in our own 

 Southwest ; in the Rockies where Notliolaena and CheUanthes 



