ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 439 



by their elongated parenchymatous form and thickened walls, but by dots 

 resembling longitudinal or oblique fissures. They are thus adapted for 

 special mechanical purposes, either to resist flexion and traction, as in the 

 rhizomes of Polytrichum, or for local strengthening. 



(3) The absorbing system is especially represented by the rhizoids, 

 which display no less adaptation for this purpose than root-hairs. In the 

 saprophytic mosses this adaptation is particularly strongly displayed in 

 haustorium-like structures (^EurJiyncJiium prselongum), perforating appendages 

 (^Wehera nutans), or a structure resembling the hyphse of fungi (Buxbaumid). 

 The foot of the sporogonium is usually provided with a papillose absorbing 

 tissue. 



(4) The assimilating system, frequently imperfectly developed in the 

 leaves, is sometimes developed in its most perfect form in the capsule as a 

 palisade-tissue {Funaria Jiygrometrica, Bryum argenteum, &c.) ; sometimes 

 also as a spongy parenchyma rich in chlorophyll (Physcomitrium pyriforme, 

 Zygodon Forsteri) ; or there are intermediate forms, as in Wehera elongata 

 and Meesia longiseta. 



(5) The conducting system consists of simple or compound cauline 

 bundles, and of foliar bundles with or without leaf-traces. The latter have 

 blind endings in the cortex of the stem (Mniuni), or unite with the cauline 

 bundle (Splachnum, Polytrichacese). The seta almost always possesses a 

 conducting bundle. The simple central bundle consists entirely of aqui- 

 ferous cells which may be regarded as trache'ids of the simplest kind. 

 Their walls are usually thin and smooth, but there are sometimes delicate 

 reticulate sculpturings in the ends of the bundles (Mnium punctatum, Bryum 

 leucotrix). The compound bundles of the PolytrichaceEe belong to the 

 concentric type. The central hadrome bundle either consists entirely of 

 aquiferous cells {Pogonatum, Polytrichum), or also of an intercalary con- 

 ducting parenchyma (Atrichum undulaturri). In Dawsonia su'perha and the 

 rhizome of Polytrichum, the central cylinder is composed of aquiferous 

 cells and a mechanical tissue. The leptome-sheath is chiefly employed in 

 the conduction of albuminoids, and consists, when most completely differ- 

 entiated, of sieve-tube-like rows of cells, between which are cells resembling 

 cambiform (^Polytrichum juniperinurri). In the seta the central bundle is 

 sometimes surrounded by a well-developed protecting sheath (Funaria 

 hygrometrica, Meesia longiseta). 



(6) The reserve-system is represented by the aquiferous tissue usually 

 present in the capsule, and by small tuberous reservoirs of reserve-material, 

 which occur in some species as shortly stalked appendages to the rhizome 

 or protonema, as also in the parenchyma of the stem of Buxbaumia. 



(7) The aerating system is typically developed in the sporogonium. The 

 stomata often entirely resemble those of flowering plants in their structure 

 and mechanism. 



(8) No secreting or excreting organs have as yet been discovered in 

 Mosses. 



The author gives a special description of several saprophytic mosses. 

 Buxbaumia he describes as entirely destitute of assimilating leaves. 

 Finally he discusses the phylogenetic relationship of the various forms of 

 Musci. 



Homologies of Mosses.* — M. P. Vuillemin objects to the term alter- 

 nation of generations as applied to mosses ; he regards their stages of 

 development rather as a kind of metamorphosis. In the evolution of a 

 moss there are three phases : — (1) The thallophytic phase, reduced to what 



* Vuillemin, P., ' Sur les homologies des Mousses,' 59 pp., Nancy, 1886. 



