Physiologie. — Palaeontologie. 489 



min infolge sekundärer Prozesse bei der Eiweissdissimilation gebildet 

 werden, kürzer oder länger gespeichert bleiben und dann^ wieder 

 zur Eiweisssynthese benutzt werden. Aus dem Charakter einer 

 ökonomischen Form des Stickstoffspeicherung lässt sich die starke 

 Ansammlung in den Samen erklären. Autorreferat. 



Benson, M., Miadesmia tnembranacea Bertrand; a new Palaeo- 

 zoic Lycopod with a Seed-like Structure. (Phil. Trans. Roy. 

 Soc; Ser. B. Vol. 199. p. 409—425, with 5 plates, and a figure in 

 the text. 1908). 



This plant, the first herbaceous Palaeozoic Lycopod known struc- 

 turally, was exceedingly minute. Its stem was slender and without 

 an}^ trace of skeletal or secondary tissue. The megasporophylls show 

 a more advanced ly^g^ of seed habit than has hitherto been met 

 with in Cryptogams. The megasporange gave rise to a Single, thin- 

 walled Spore, which in development and structure resembles an 

 embryo-sac, and germinates in situ. An integument or velum sur- 

 rounds the sporange, leaving but a small distal orifice as micropj-le. 

 This is surrounded by numerous processes of the integument, which 

 form a collecting and incubating apparatus for the microspores. 

 There is no trace of an envelope about the microsporange. The 

 carpellary leaf was shed at maturity, and resembles a winged seed. 



The foliage leaves (1—2 mm. in length and breadth) are only 

 about a third the size of the seed and are delicate, acuminate struc- 

 tures, very thin and without stomates. Thej^ are bordered with a 

 thin membrane but one cell thick. Some show multiseriate hairs 

 springing from the adaxial surface of the leaf base. The large, 

 characteristic ligule is inserted in a pit, which it fits as a cork does 

 the neck of a bottle. 



The anatomy of the stem is simple. The x^'-lem forms a simple 

 protostele, and is built up entirely of scalariform tracheides with 

 peripheral protoxylem of spiralty thickened Clements. The protoxylem 

 groups Vary from 3—6 in number. The phloem surrounds the xylem. 

 The stem bifurcated at intervals, the dichotomy being unequal. 

 The inner cortex is lacunar and trabeculae of swollen cells pass 

 radially from the central stele to the outer cortex. The latter con- 

 sists of about three layers of large cells and a small-celled peri- 

 pheral layer. 



The mature megasporophj'll was a relatively bulky structure, 

 the lamina being bordered by a characteristic membrane, only one 

 cell thick, The character and insertion of the ligule resembles that 

 of the foliar leaf, and the structure of the axis of the cone ma}' be 

 closely compared with the vegetative axis. In the mature megaspo- 

 rophyll the vascular bündle traverses the leaf-base, and then, sinking 

 abruptly at the base of the sporange, travels up the midrib of the 

 lamina. The sporange, attached by its cylindrical pedicel to the 

 leaf-base, lies slightly inclined to the plane of the lamina, which 

 extends a considerable distance beyond it. The wall of the sporange 

 is several layers of cells in thickness, and within, the thin coat of 

 the Single megaspore may be seen. The sporange is prolonged into 

 a beak-like process, and is roofed over by a velum, in which the 

 aperture is distal. 



The immature megasporophylls are also described. The micro- 

 sporophylls, some of which show ripe spores, have the tj'pical ligule 

 of Miadesmia , and are intermediate in size between the foliage lear 



