

466 



MR. T. JOHNSON ON THE SYSTEMATIC 



(1889), showed that the asexual non-motile spores of the Tilo- 

 pteridece * (a group placed by all phycologists in the Phteophycea) 

 are quadr {nucleate, and in reality potential tetrasporangia. At 

 the same time that this discovery helps one to withdraw the Die- 

 tyotacece from the Floridece, with which Falkenberg hesitatingly 

 placed them, it does not of itself render the opinion entertained 

 by some observers, that the Dictyotacece lead on from the Phao- 

 phycece to the Floridece, untenable. In Dictyopteris polypodioides 

 the tetrasporangia are in sori arranged along the midrib, the 

 tetrasporangia in Dictyota dichotoma being scattered over the 

 surface of the thallus. 













B. Sexual. — i. Antheridia. 



uret 



in Dictyota t, tracing them from origin to maturity. It would 

 not be correct to say that, up to the present, the antheridia of 

 Dictyopteris have not been observed. Beyond the statement in 

 'Etudes Phycologiquea,' that the antheridia in Dictyopteris, 

 Taonia, Padina, and Spatoglossum are of the same type as those ol 

 Dictyota, I have been able to find no description or figures of those 

 of Dictyopteris J. They occur both alongside the midrib and scat- 

 tered over the general thallus-surface on each side of it (PI- XIII- 

 fig. 4). Each antheridium, of no definite outline, consists of 3 to 

 100 transparent adjacent superficial cells of the thallus. These 

 cells acquire clear granular contents, come to project a little 

 above the thallus-surface, and divide tangentially into small stalk- 

 cells and large outer cells. The contents of the latter undergo 

 repeated divisions until there is formed a small-celled tissue of 

 compact cubical cells, each containing a potential " polliuoid, 

 the whole being compared by Thuret in Dictyota to the young 

 antherozoid mother-cells in the antheridium of a moss. -Each 

 antheridium has, in Dictyopteris, only a feebly developed in- 

 volucre, quite insignificaut compared with that of DictyoU 

 (figs. 1, 5). At maturity the outer wall of the antheridium is 



ru 



§ say 



s "the cor- 



w _ ^ c 



escape into the surrounding water. Thuret , 



puscles which escape from the cells of the antheridium in Dictyota 



w 



Reinke, in Bot. Zeit. t. ii. & iii. nos. 7-9 (1889). 

 t J. Thuret, in Ann. <L Sc. Nat. 4 e ser. Bot. t iii. (1855). 



X Agardh, ' Species Algarum,* i. p. 115 (1848). 

 " Thnret, op. cit. p. 11 . 







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