©® 



212 DIPTEROID FERNS [CH. 



felt, as in P. biformc Bl. [= P. coronariiuti (Koenig) Desv.], where it covers 

 the discoid, cake-hke fertile lobes, protecting the young sporangia. The 

 origin of the sporangia is almost simulta- 

 neous, but yet slight differences in time 

 are indicated by their relative size, as 

 seen in Fig. 720. The adult sporangium 

 is shown in Fig. 721. Here the stalk 

 consists of only three rows of cells, as 



against the four rows in Cheiropleiiria. ^'^^^id^ b 



This is, however, not an essential differ- 

 ence, though important for comparison 

 elsewhere. The sporangia of Platyzoina 



show both types (see Vol. II, Fig. 492). pig_ „^j_ ^^^ .sporangium of Platycerium 



Moreover there is an inherent probability aethiopkum as seen from the side. /^ = trans- 



, , _ ,, . .. verse sections of its stalk. ( x 80.) 



that the change should follow m any hne 



of descent where reduction of the sporangium is involved. While the spore- 

 output in Cheiropleuria is typically 128, that in Platycerium is only 64. But 

 the size and spore-output are not absolutely determining causes of the change 

 of structure: in Dipteris, with smaller sporangia and an output of 64 or less, 

 the four-rowed stalk is retained. The sporangium of P/^/j/fffr/z/w is pear-shaped, 

 and the annulus, which consists of more numerous cells than in Cheiropleiu'ia, 

 shows only slight obliquity, and is almost interrupted at the insertion of the 

 stalk, though not actually so. These facts collectively indicate for Platycerium 

 a more specialised state than in Cheiropleuria, but they indicate a type 

 cognate with it. There is no perispore in Platycerium (Hannig, /.<:.). 



The sporangia of Platycerium alcicorne show considerable regularity of 

 orientation, so that the plane of the annulus cuts the direction of the 

 underlying vein at right angles. They originate for the most part simul- 

 taneously, and in two rows, as though each sorus were an extension of a 

 simple radiate-uniseriate sorus. This may very probably have been the 

 original source. 



The germination in Platycerium has been observed by Bauke (yBot. Zeit. 

 Bd. XXXVl) and by Von Straszevvski {I.e. p. 272). The young prothalli are 

 at first filamentous and often branch early, but the filaments develop 

 unequally. A flattened expanse is soon formed laterally, or more than one : 

 these bear pluricellular glandular hairs on the lower side, as in the 

 Cyatheaceae and in Diacalpe. The prothalli are sometimes dioecious, but not 

 always. The fact that the lid-cell of the antheridium is here divided, as it is 

 in IVoodsia, suggests, as do also the glandular hairs, a relation to other 

 relatively primitive Ferns, and in particular to the Cyatheoids. The hairs 

 are similar to those first borne on the sporeling, while in the latter an early 

 apospory was seen to follow on mechanical damage to the young leaf. Such 



