XXXIII] 



SPORANGIA 



301 



an increasing precision of the stomium, which in Hemitdia, Alsophila and 

 Metaxya consists of a compact group of four cells, while in Lophosoria it is 

 ill-defined. Thus the sporangium of the Cyatheaceae is more precisely con- 

 structed than that of Lophosoria, and still more than that of Gleichenia, though 

 G dichotoma and Platyzoma show features of size and construction that are 

 sucTcrestive for comparison. The spore-output per sporangium is low. In 

 Alsophila it is typically 64, as it is also in Lophosoria and Metaxya. But all 

 of them fall far short of the large numbers in the Gleicheniaceae (excepting the 

 aberrant Platyzoma). Cyathea mcdnllaris also has 64 spores per sporangium : 



h:^ 



msB, 



Fie. .6^ Sporangia of Cyatheaceae. a, ^,/^^- Fig. 564- Alsophila atrov:rens Vr^^X. 



%Udia catmsihx. «, presents the distal or A young sorus cut ver ically , and .ho n - 



pertheaffae ^^ -g ^ .^'ight mdication of bas.peta 



S'eEum. (x'loo.) ., d, e' Alsophila succession of the sporang.a. ( x :oo.) 



excelsa Br. c, presents the basal or proximal 

 face, d, shows the stomium with the distal 

 face downwards. e,showsatransverse section 

 of the stalk, (x loo.) 



but in C. dcalbata such low numbers as 16 and even 8 have been recorded 

 from the single sporangium. These facts show that the Cyatheaceae are a 

 family of increasing precision but of reduced complexity of the sporangium, 

 while the extreme is reached in Cyathea dcalbata. They strengthen the view 

 that this genus is more specialised, while Alsophilq is less specialised, and that 

 Llemitelia takes a middle position. 



The development of the sorus has been observed in all three genera In 

 Alsophila atrovirens it first appears as an upgrowth of the leaf-surface 

 (Fig. 564). Upon the receptacle thus formed the sporangia and hairs appear 



