264 SUMMARY OF CURRENT RESEARCHES RELATING TO 



without transverse articulations ; but iu tho Arthrodonteae tho teeth are 

 articulated. 



An internal peristome has never been observed in the Aplolepideae ; 

 it is present, however, in nearly all the families of the Diplolepideae. 

 The internal peristome is composed of two membranous lamina), but tho 

 plates composing each lamina are thinner, softer, more difficult to 

 separate, and often more difficult to distinguish, than is the caso with 

 tho corresponding plates in the external peristome. In some species, 

 however, tho lines bordering the plates form two rosettes which are 

 easily distinguishable. The plates which are placed on the dorsal 

 face of the external peristome correspond to the ventral plates of tho 

 teeth ; they are the same in number, and are exactly opposite to the 

 latter. There is thus at each stage of elevation of the internal peristome 

 a circle of sixteen plates, which originate in the same layer of cells as 

 the ventral plates of the external peristome ; they represent the internal 

 vertical divisions of these cells, the ventral plates of the teeth being the 

 external divisions. The horizontal divisions are represented by lamellae 

 which project at the articulations. In certain species these lamella) of 

 the teeth adhere to the internal peristome, and the primitive cells remain 

 entire, except on their lateral faces where a thickening of the divisions 

 occasionally takes place. The internal peristomial membrane, which 

 remains undivided in its lower part, shows a dorsal network formed of 

 sixteen vertical equidistant lines, and numerous horizontal lines which 

 are parallel and very near to one another. The author takes Milium 

 ortliorrhynchum as an example of the species in which the two networks are 

 easily distinguishable, and describes their structure somewhat in detail. 

 If a transverse section be made of a young capsule of 31. orlhorrhynclium 

 a little above the point where the two peristomes originate, we see them 

 not as two concentric circles, but as sixteen semi-cylindrical cavities. In 

 the interior of these cavities the ventral lamellae of the teeth arise hori- 

 zontally in the form of semi-elliptical plates, without touching the 

 membrane that surrounds them. 



We have here then the sixteen series of primitive cells from which 

 the two peristomes are formed ; but on account of the unequal thickening 

 of their different elements the two systems of plates of which they are 

 composed cease to adhere together, and they become free. 



Hybrid Mosses.* — Dr. C. Sanio records the occurrence of hybrid 

 mosses in the section Harpidieae, viz. between Hypnum Jluitans and 

 aduncum, and between H. lycopodioides and jluitans, giving rise to a great 

 variety of forms. In only one of these did the vegetative organs present 

 a true species ; in the remainder the hybrid character was manifested, 

 especially in the vegetative portions, while the fructification was very 

 little or not at all altered. 



Distribution of Hepaticee.f— Dr. C. Massalongo classifies the Italian 

 species of Hepaticae ; first, according to their habitat, viz. (1) aquatic 

 (Biccia Jluitans and natans) ; (2) calcicolous ; (3) silicicolous ; (4) sapro- 

 phytic ; (5) hygrophilous ; (6) xerophilous ; (7) indifferent. Secondly, 

 they are classified according to altitude ; and thirdly, geographically, 

 according to the other countries of Europe in which they are found. 

 A useful epitome of the structure of the various organs is appended. 



* Hedwigia, xxvi. (1887) pp. 194-214. 



t Atti Congr. Naz. Bot. Critt. Parma, Sept. 1887, pp. 13-27. 



