IX MARATTIACE^—ISOETACE^ 271 



leaf of A. evecta, which has much the same structure as that of 

 Marattia. The central vascular bundle is horse -shoe shaped 

 in section, and shows a central mass of large tracheids with 

 reticulate or scalariform markings, surrounded by the phloem 

 made up of very large sieve-tubes much like those oi Botrydiium, 

 and with these are the ordinary protophlocm cells and bast 

 parenchyma. A distinct bundle-sheath is absent, as, according 

 to Holle,^ it is from all the bundles in both Jllaratlia and 

 Angiopteris, except those of the larger roots. The bulk of the 

 ground tissue is composed of large parenchyma cells, but on 

 both sides just below the epidermis is a band of colourless cells 

 which resemble exactly the collenchyma of Phanerogams. In 

 the base of the petiole this becomes harder and forms a colour- 

 less sclerenchyma, according to Holle," which in Daticea is 

 replaced by brown sclerenchyma like that of the true Ferns. 

 In the lamina of the leaf in Angiopteris too, the arrangement 

 of the tissues is strikingly like that of the typical Angiosperms. 

 A highly-developed palisade parenchyma occupies the upper 

 part of the leaf beneath the epidermis, which bears stomata only 

 on the lower side of the leaf. The rest of the mesophyll is 

 composed of the spongy green parenchyma found in the other 

 Ferns. The smaller veins both here and in Marattia have 

 collateral bundles. 



TJie Sporangia 



The sporangia of the Marattiacea; differ most markedly 

 from the Ophioglossaceae in being borne on the lower side of 

 the ordinary leaves, and not on special segments. Except in 

 Angiopteris^ they form synangia, whose development has only 

 been studied in Marattia? Luerssen describes the process 

 thus : "In Marattia the first differentiation of the sporangium 

 begins while the young leaf is still rolled up between the 

 stipules of the next older one. The tissue above the fertile 

 vein is more strongly developed than the adjoining parenchyma, 

 and forms an elevated cushion parallel with the vein. This is 

 the receptacle, which develops two parallel ridges, separated by 

 a cleft. These two ridges grow up until they meet, and their 

 edges grow together and completely close the cleft which lies 

 between. In each half there are differentiated the separate 



^ HoUe (2), p. 216. - Holle (2), ibid. ^ Luerssen (7), vol. i. p. 579. 



