468 



INTRODUCTION TO CRYPTOGAMIC BOTANY. 



and some of the very finest forms, as the larger SplacJma, 

 are found in high northern latitudes, where, however, the heat 

 of the short summer is often considerable. A very few only 

 of the tribes are excluded from Europe. Particulars will be 

 given under the respective tribes. They grow in all kinds of 

 situations, and a few flourish where very little light penetrates. 

 Many luxuriate under water, but seldom fructify. A few 



Fig. 100. 



a. Vertical section of the sporangium of Atdacomnion palustre, after 

 Lantzius-Beninga, to show that the outer row of teeth arises from the 

 inner layer of the cells, which constitute the outer wall of the sporangium, 

 and the inner row from the outer layer of the spore-sac. This, it should 

 be observed, is connected with the outer wall by threads traversing 

 the intermediate cavity. It will be seen that the teeth in either case are 

 formed by the thickening of the walls of two contiguous cells. 



h. Tip of leaf of Calymperes Afzelii, with gems attached to the end 

 of the nerve. In Calymperes rigida the gems are attached to the very 

 tip of the lea£ After a sketch in Hook. Herb. 



