CRYPTOGAMIA IN CULTIVATION. 51 



been much confused ; they are distinguished by their different 

 modes of fruitiug, "We will consider their cultivation farther on, 

 in connection with the ferns, but I would here suggest, as a topic 

 for discussion, the question why it is that the Lycopodiums are 

 cultivated only with great difficulty, while the Selaginellas are 

 managed with the greatest ease. Marsilia quadrifoUa, a native of 

 Connecticut, has been cultivated at the Botanic Garden, and has 

 become established in ponds in this vicinity ; the leaves resemble 

 those of an oxalis ; they float upon the water, the spores being at 

 their bases. The plant is perfectly hardy, very pretty, and grows 

 quite rapidly. 



Equiseiums, or Horse-tails, are an interesting and neglected 

 genus. For out-door work nothing can be better, for certain 

 effects, than the E. sylvaticum. It is not rai'e in our woods, and 

 can be transplanted without much difficulty. It is already in use 

 in England, and why not here ? Other species of Equisetum are 

 good, but none compare with this among our natives ; it grows 

 from twelve to eighteen inches high. 



Ferns are more largely represented in cultivation than all other 

 cryptogams ; they vary in size from some species of Trichomanes, 

 which are not half an inch high, to the noble Dicksonia antarctica, 

 which attains a height of from sixty to eighty feet, with a spread- 

 ing crown more than one hundred feet in circumference, yet in 

 each of these extreme cases they grow from spores, which, even 

 under the microscope, show but a very slight difference in form. 

 A few notes on the introduction and cultivation of exotic ferns in 

 Europe may be interesting. 



The first species taken to England were Cystopteris btdbifera and 

 AcUantum pedatum. They were carried thither from Virginia by 

 John Tradescant, in 16*28. Two other American species, Onodea 

 sensibiUs and Camptosorus rhizophyllus, were introduced prior to 

 the year 1700. 



In 1768 there were at Kew 10 exotic species. 

 " 1789 " " " " 34 " " 

 " 1813 " " " " 83, at Berlin 30. 



" 1822 " " " " 40, " " 91. 

 u 1846 " " " " 384. 



In 1850, eight hundred and fifty species were under cultivation 

 in Europe, and in 1866 more than a thousand at Kew alone. To 



