246 ORTHOTRICHACE^E. 



One or two points must be noted in connection with the study 

 of these plants. In the first place in order to ascertain the true 

 form of the capsule it is necessary that it should be immersed in 

 water for at least 12 hours previously, and that perfectly ripe yet 

 not too advanced capsules should be chosen for the purpose. As, 

 however, this is a somewhat tiresome process, and as the British 

 species are not as a rule dependent on this character for their 

 distinction, I have laid as little stress as possible on the form of 

 the mature, moistened fruit. 



Another point of importance is the direction taken by the dry 

 outer peristome. This falls under three main heads ; it may be 

 more or less erect or spreading stellately ; or it may be reflexed 

 closely on the surface of the capsule so as to touch it practically 

 throughout its length ; or it may be revolute, curling backwards 

 so as to form a somewhat arched curve, only touching or closely 

 approaching the wall of the capsule with its tip or upper part. 



Too much importance must not be attributed to the form of 

 the apex of the leaves. In O. rivulare and O. Sprucei it is wide 

 and rounded, in almost all the other species it tapers to a wide 

 point, which is variously obtuse or sub-acute, often differing much 

 in different leaves of the same stem. In certain species such as 

 O. tenellum it is usually more obtuse, while in most the acute 

 form predominates, but as a rule it does not afford a sufficiently 

 marked or constant character for specific distinction. 



A very important and useful character in the diagnosis of the 

 species is to be found in the stomata which are found in all the 

 species scattered here and there on the capsule, almost always, 

 but not invariably, about the level of the base of the spore-sac. 

 They may be superficial (Tab. V. fig. 1), when the two oval or 

 remform guard-cells are entirely displayed ; or immersed (Tab. V. 

 fig. 2), when the guard-cells are more or less hidden by over- 

 lapping superficial cells. In order to see the sLomata to advantage, 

 it is best to separate a ripe capsule in the middle of the neck, cut 

 it longitudinally in two, separate the spore-sac and get rid of the 

 spores, and place it with the outer {i.e. the convex) side upwards 

 on the glass, warming it if necessary over the spirit lamp to get 

 rid of air. 



The British species fall naturally into the following sections. 



A. RUPESTRIA. Leaves with recurved margins ; not hair- 

 pointed. Peristome teeth erect or spreading when dry. Stomata 

 superficial. O. rupestre. 



B. CUPULATA. Leaves with recurved margins ; not hair- 

 pointed. Peristome teeth erect or spreading when dry. Stomata 

 immersed. O. anomalum, O. cupulatum. 



