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EUROPE AND NORTH AMERICA. 



17 



these cells Mr. Mitten uses the term spatia or spaces. Tuis 

 description applies to the leaves of the branches, but in those of 

 the stem and perichaetium the two kinds of cells are not so distinct, 

 as the chlorophyl is wanting and the hyaline cells are often 

 extremely narrow, especially those at the margin, where they 

 generally form a more or less wide border. 



The stem leaves in all the European Sphagna differ considerably 

 from the branch leaves both in form and structure ; they are 

 distant from each other, with a \ arrangement, or five leaves in two 

 spiral turns, and are generally reflexed against the stem, as if 

 pushed back by the descent of the pendent branches. Their form 

 is oblong, ovate, or Ungulate, and at their basal angles there 

 are generally present more or less evident auricles ; they, are also 

 very uniform on the same plant both in size and shape. The 

 areolation is laxer than that of the branch leaves, and spiral fibres 

 are rarely present in their hyaline cells ; the basal cells form one 

 or more rows of incrassate vesicular cells, more or less coloured, 

 but the greater part of the leaf is colourless from the absence of 

 chlorophyl in the narrow cells. 



The branch leaves are small and closely imbricated, and differ 

 considerably on the two kinds of branches, and even on different 

 parts of the same branch ; on the divergent branches they are 

 small at base, becoming larger in the middle of the branch, and 

 narrower and more distant towards the point ; the three or four at 

 the extreme base of the branch are very small and have a peculiar 

 shape, being somewhat obliquely triangular in outline, and partly 

 resemble the stem leaf in areolation ; in fact, they convey the idea 

 of one half of a stem leaf which has been split down the middle, and 

 possibly may originate by being torn apart by the separation of the 

 branches forming the fascicle, at their first stage of development. 



Russow attaches importance to these leaves, and names them 

 intermediate leaves, but they are not always alike in the same 

 species, nor do they offer much variety in different species, and 

 they have always a broad border of narrow cells ; the leaves of the 

 pendent branches are all longer and narrower, as are also their 

 component cells. 



The relation of the two forms of cells to each other, in the 

 anatomy of the ramulire leaves, is a point of great importance, 

 since it originates in the fundamental formation of the leaf, and it 

 therefore takes part in the diagnosis of species ; to observe this 



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