INTRODUCTION TO CRYPTOGAMIC BOTANY. 561 



641. Though many species of LycopodiuTri are found in 

 tropical and subtropical countries, it is far less addicted to 

 warm localities than Selaginella, which does not occur at all 

 in New Zealand or Great Britain, though both countries con- 

 tain many species of Lyeopodium. Lycopodiwm alpinum 

 and Selago are fond of a moist cold climate, and it is only in 

 high latitudes that they appear in the plains, while on the 

 contrary L. inundatum forms large patches in the marshes of 

 the south of England. New Zealand has far more species 

 of Lycoiwdiuni than Great Britain, and several of them are 

 amongst the noblest of the genus, and may be regarded as 

 tropical forms. A curious instance of the appeai'ance of a tro- 

 pical species in temperate latitudes is afforded by L. cernnuTn, 

 a species very widely diffused in the tropics. It occurs about 

 the warm springs of the Azores in Terceira and St. Michael's,* 

 in spots exposed to the sun, and again in the southern island 

 of St. Paul, a fact which has its parallel in the occurrence of a 

 tropical Pteris under similar circumstances in a small island in 

 the Mediterranean. T'tnesi'pteris is widely diffused in the 

 southern hemisphere, extending to California, and often grows 

 on the trunks of tree ferns ; and PsilotuTii extends through 

 most of the tropics, and reaches the Southern United States 

 through Brazil and Central America. 



64!2. The degree to which some of the species vary is admi- 

 rably illustrated in Dr. Hooker's Memoir. Figures are given of 

 Lyeopodium densum under different forms which grow inter- 

 mixed in New Zealand. One is densely fastigiate, with 

 broadish ovato-lanceolate leaves, closely appressed to the stem ; 

 in the second the habit is diffuse, the leaves narrow, far 

 more elongated, and not at all appressed, so that the plant 

 looks squarrose ; but even in this form the leaves are very 

 different in different parts of the stem ; in the third form the 

 branches are all slender and clothed with narrow appressed 

 leaves, which are sometimes imbricated, sometimes disposed in 

 whorls. The student, therefore, must be prepared for patient 



* The ticket which accompanies the sjiecimeus in the Hookerian 

 Herbarium states that the temperature of the water was 114^, the air 

 at the same time being at 65°. 



36 



