XX] 



SORI 



One of the most striking of these fossils is Ptychocarpiis {Pecopteris) unitits 

 Brongn., from the Upper Coal Measures of France. Here on the lower surface 

 of the pinnules of a Pecopterid leaf the sori are disposed in a row on either side 

 of the midrib. Each is a synangium composed of about seven sporangia united 

 upon a common receptacle. The form is that of a truncated cone with a 

 slight terminal dimple. Centrally there is a vascular strand connected 

 with the system of the leaf. The 

 sporangial wall consisted of about 

 four layers of cells, and there was no 

 annulus. Dehiscence appears to have 

 been by terminal pores, and the 

 number of spores in each sporangium 

 was very large, probably equal to that 

 of the modern Christensenia (Fig. 

 407). The correspondence with this 

 genus is very close indeed, the dif- 

 ferences being of degree only. But the 

 leaf-blades that bore them were very 

 different. 



Certain Pecopterid forms from the 

 Coal Measures have been included 

 under the name Danaeitcs, and their 

 sori are described as synangial and 

 linear, consisting as in Dauaea of 

 two rows of fused sporangia each 

 dehiscing by an apical pore. But 

 Seward {J.c. p. 398) discredits this 

 conclusion on the ground of lack of 

 detail. On the other hand, Halle's 

 description of the Rhaetic Fern 

 Danaeopsis (A rkiv for Botaiiik, Band 

 1 7, No. I ) shows that notwithstanding 

 its name the sori of this Fern are 

 composed of separate sporangia. The 

 venation of the lanceolate pinna is 



Ptychocarpiis itnitiis. Fructification. 

 ^, part ofa fertile pinnule (lower surface), showing 

 numerous synangia. B, synangia in side-view. 

 ( X about 6.) (After Grand 'Eury.) C, a synan- 

 gium in section parallel to the surface of the leaf, 

 showing seven confluent sporangia, a, bundle of 

 the receptacle : b, its parenchyma : t, tapetum : 

 d, spores: e, f, common envelope of the synan- 

 gium. (x about 60.) (After Renault, from .Scott's 

 Studies.) 



forked, but the branches anastomose. The sporangia are arranged in double 

 rows facing one another, dehiscence being by slits as in Augiopteris. But it 

 appears that the relation between the sori and the veins is not so regular as 

 in the recent Marattiaceae. The spore-counts approach the estimate for 

 Angiopteris. But Halle sees in Danaeopsis a resemblance more nearly to 

 Archangiopteris (Halle, Figs. 2, 7, 12) (Fig. 408). 



It thus appears evident that the Marattiaceous type of sorus was already 



