VEGETATIVE KEPKOD UCTION. 



235 



pollen, and the mcgaspores are called embryo-sacs:'^ The mi- 

 crosporangia and megas[)orangia, also, are always different in 

 form and structure, and the leaves upon which they are visually 

 borne are also of two distinct forms. In no case do sjjoro- 

 phylls perform nutritive work ; they are always specialized. 

 Those leaves which bear microsporangia are called slavicns, 

 and the leaves which produce the megasporangia are called 



Fig. 242. — .T , a microsporangium of Salvinia seen from the outside. It contains (^^ 

 microspores. B,io\xr spores from W, surrounded by liardened frotliy mucilage. C, 

 median lon.ti^tudinal section of a megasporangium, showing structure of wall at matu- 

 rity, and tlie single spherical megaspore. with its proper wall {black line) and a thick 

 frothy epispore lU 30S1. A and C magnified 55 diam. B, magnified 250 diam. — After 

 Strasburger. 



carpels''-'- (figs. 245, 250, 251). In spite of these special 

 names, it must be carefullv borne in mind that the sporangia 

 and sporoph3'lls of the seed plants are not different from those 

 of the fernworts or mossworts in any essential particular, 



329. The sporophylls of the seed plants are usually aggre- 

 gated by the failure of the internodes of the axis to lengthen 

 as much as between the foliage lea\'es. Very often, also, the 



* These special names were given because the seed plants were 6rst 

 studied, and it was long before the real nature of the parts and their rela- 

 tion to similar ones in the lower plants were known. The terms are still 

 in use, and are likely to continue to be used for convenience. 



