TKANSACTIONS OF SECTION D. 745 



The primary development ceases for a considerable time before the cambium appears. 

 The formation of secondary tissue is at first most active at the sides of the cylinder. 

 At its narrow edges the process begins later, and for a long time is less active. 

 Hence the vascular cylinder gradually acquires a circular transverse section. The 

 secondary vascular bundles are concentric ; their xylem consists chiefly of long 

 tracheides, -which have a tortuous course, and arise, like those of Dracana and 

 Yucca, by the elongation of single cells. 



Here, as in other Monocotyledons, the cambium does not form a single initial 

 layer of cells, but rather constitutes a secondary meristematic zone in which 

 several layers may successively take up the cambial divisions. 



The first -formed periderm is external at the sides, internal at the prominent 

 edo-es of the flattened stem. This helps to give the older stem a cylindrical form. 



At a later stage successive interniil periderms arise, and soon the whole of the 

 primary corte.x is thrown oil". This is meanwhile replaced by the formation of 

 abundant secondary cortex on the outer side of the cambial zone. The outer 

 layers of the secondary cortex also are successively cut off as bark. 



It is evident that a process of secondary growth of the same general type has 

 appeared independently in several distinct groups of Monocotyledons. 



3. On, tlie Simplest Form of Mosses. By Professor Dr. Goebel, For.F.L.S. 



Since Hofmeister's researches proved that the moss sporogonium is the homo- 

 logue of the leafy spore-forming fern-plant, and the sexual moss-plant is the 

 Lomologue of the fern prothallus, it has been the endeavour of many morphologists to 

 discover how the transition from the moss sporogonium to the fern-plant took place. 

 These eflorts have, however, led to no result. They started from the assumption 

 that vascular cryptogams sprang from moss-like ancestors. My investigations 

 early led me to regard such a view as erroneous, and to the conclusion that mosses 

 and ferns do not stand in direct genetic connection, but have been derived from a 

 common stock. The character of this alga-like ancestor we must seek for in the 

 sexual generation, whilst the asexual generation in the moss series and in the fern 

 series has developed differently. 



Now we see the sexual generation of the moss beginning as a simple structure 

 ■ — the protouema — often mistaken for a filamentous alga. A similar structure is 

 found in the prothallus of Hyuienophyllere, and in the beginning of the development 

 in the prothallus of most other ferns. The moss-plants arise out of the protonema 

 as lateral shoots. They were originally only the supports of the sexual organs, for 

 the protection of which envelopes were formed. If, now, the sexual organs were 

 developed, not coincidently with the formation of the moss-stem, but only at a 

 later period, then the envelopes of the sexual organs might serve for assimilation 

 as leaves, and thus might arise the moss-plant as we have it now. 



The simplest moss-plant was, then, one in which the sexual organs were seated 

 on the protonema, surrounded by one or several leaf-like envelopes. Such a form 

 has hitherto been hypothetical, but I have had the good fortune to discover its 

 ■existence in Buxbaumia. 



The male plants of this moss are of a wonderfully simple character, and corre- 

 spond exactly with the hypothetical form just referred to. From primary delicate 

 protonema-threads a thicker branch takes origin, at the end of which is a single 

 antheridium, long-stalked like that of a liverwort, and corresponding otherwise in 

 form with that of liverworts. 



Around this antheridium is a curved shell-like envelope, which has no chloro- 

 phyll, and difters also from other known moss-leaves in the arrangement of its 

 cells, there being no two-sided apical cell. No stem is formed, the only indication 

 of it being the formation of one or two oblique segment walls in the cell beneath 

 the leaf-insertion. 



The female plant is more highly developed, as one would expect from a bio- 

 logical point of view. The formation of the embryo demands a considerable food 

 eupply, and therefore a cell mass of some bulk must be developed. A similar 

 arrangement to the one I describe is seen in the filamentous prothalli of the 



