102 PRINCIPLES OF PLANT-TERATOLOGY. 



increase of synangia (fig. 111). These casee are almost 

 certainly reversions, as Thomas suggests, to the more 

 complex type of sporophyll met with in the ancient 

 Sphenophyllales ; for in both Clieirostrobus and Spheno- 

 phyllum (certain species) the sporophyll is repeatedly 

 forked, and moreover the sporangia are borne on special 

 stalks or sporangiophores. It is now generally admitted 

 that the nearest modern relatives of the Spheno- 

 phyllales are to be seen in the Psilotacese. We have 

 here, therefore, another excellent instance of the light 

 which may be thrown by abnormalities on the ancestry 

 and morphological nature of highly modified, and on 

 that account, obscure and inexplicable structures. 



Fia. 112. — Cerastium glomeratum (Mouse-ear CHelrweed) . Two 

 nucelli (megasporangia) in one ovule (longitudinal section). 

 (After Miss Gibbs.) • 



b. Sporangia. — In Ginkgo it is not uncommon to find 

 stamens bearing three or four, instead of the usual two, 

 pollen-sacs. Undoubtedly a reversion to the condition 

 in the ancestry where the sporophyll was much better 

 developed and on a larger scale. 



The presence of two nucelli (megasporangia) in an 

 ovule is of not very infrequent occurrence. Hofmeister 

 cites it as occurring in ]\[orv.'i alba. Misses Benson and 

 Sanday in Carpinns Betnlns, and Miss L. S. Gibbs in 

 Gerasfinni (fig. 112). 



Bower observed a very rare case in Lycopodinm 

 rigvhuu, in which two sporangia were present on the 

 sporophyll instead of the usual single one (PI. XXXVIII, 

 fig. 2). 



