XIV INTRODUCTION. 



very nearly so, occurring very rarely, perhaps exceptionally, in 

 the pleurocarpous species. 



The tertile flowers are always more or less gemmiform, i.e., 

 bud-shaped ; the male flowers are occasionally wider, with open 

 and more or less spreading bracts ; in this case they are termed 

 discoid. 



Upon fertilisation the archegonium and its contents undergo 

 great development ; the oosphere becomes the capsule or sporan- 

 gium, the outer part of the archegonium itself simultaneously 

 developing up to a certain point, but ultimately rupturing midway 

 so that the upper portion is carried up with the fruit, the lower 

 half remaining fixed at the base and forming a minute sheath 

 round the base of the fruit-stalk, termed the vaginula ; this is 

 occasionally covered with short, erect hairs (Tab. V. 12). 



In very few cases the capsule remains sessile ; in the vast 

 majority of species it is elevated on a seta, or fruitstalk, of vary- 

 ing length ; and it is by this process of elevation that the arche- 

 gonium is ruptured. The upper half as has been mentioned is 

 carried upwards with the fruit, and is known as the calyptra or 

 veil ; it is usually 01 a thin membranous texture, more or less 

 completely covering the capsule, and either falls off before the 

 capsule is fully ripe or in other cases remains till maturity ; the 

 increase in size of the capsule usually causes it to split from the 

 base upwards ; when the fission takes place on one side only, or 

 conspicuously on one side most strongly, the calyptra is said to be 

 cucullate, i.e., hood-shaped (Tab. IV. 2, 6) ; when it splits equally 

 on two, three or more sides it is termed mitriform (Tab. IV. 1). 

 The calyptra may be smooth or plicate, glabrous, papillose or 

 hairy, the hairs either erect or pointing downwards. 



The seta is variable in length and stoutness, occasionally 

 rough with warts or papillae, usually twisted when dry. It is 

 straight, flexuose, or arcuate, i.e., curved like a bow ; the curving 

 is sometimes even more pronounced, when it is said to be 

 cygneous, i.e., curved like a swan's neck. In the latter cases it 

 frequently becomes erect when old, and in some species it always 

 takes an erect position when dry, while regaining its curved form 

 when wetted. 



When dry the seta is usually spirally twisted, and the 

 twisting may be either to the right (,'.*., the spirals ascend 

 towards the right to an observer supposed to be standing within 

 the spiral ; from the outside they appear, on the side nearest him 

 to ascend to the left), or to the left. It is rarely, however, I 



