8 Splacknidium rugosum. 



1. The enormous number of the spores (500-600) compared with the 

 largest number of antherozoids contained in the antheridia of the Fucaccce, 

 i.e., 64. 



2. The large size of the sporangium compared with that of an 

 antheridium. 



3. The production of sporangia directly from the cells lining the 

 conceptacle, whereas antheridia are always borne on hairs within the 

 conceptacle. 



In the face of these facts, it is impossible to regard the sporangia of 

 Splacknidium rugosum as homologous with either the oogonia or the 

 antheridia of the Fucacece. We are, therefore, led to the third possible 

 interpretation, i.e., that they are sporangia, containing zoospores homo- 

 logous with those of the Laminariacece. It is in those very points in which 

 the sporangia of Splachnidium differ so remarkably from the oogonia or the 

 antheridia of the Fucacece that we note their striking similarity to the 

 sporangia of the Laminariacece. The size of the sporangium, its unilocular 

 nature, its single wall, the number of the spores, the size of the spores, 

 and the persistence of the empty spore cases, all point definitely to the 

 conclusion that these sporangia are homologous with those of the Lami- 

 nariacece. A comparison of fig. 6 with fig. 8 (plate III.) will show the 

 general resemblance more clearly than it can be expressed in words. 

 Whether the spores produced in these sporangia germinate directly or 

 conjugate first, or, in the latter case, whether they show any sexual 

 differentiation, are questions which can only be settled by the examination 

 of fresh material and the cultivation of the spores. 



While, then, the characteristics of Splachnidium rugosum are such 

 that it can be placed in no existing natural order of the PhaeopJiycece, its 

 nearest allies appear to be the Fucacece on the one hand and the Lami- 

 nariacece on the other. In its vegetative structure, i.e., in the nature of its 

 thallus and in the existence of conceptacles, Splachnidium bears a resem- 

 blance to the Fucacece ; it differs from them, however, in its mode of 

 growth, the former increasing by means of an apical meristem, while the 

 growth of the latter is due to divisions of an apical cell. In the presence 

 of an apical meristem Splachnidium approaches the Laminariacece, but at 

 the same time there is no plant in this order which has a cell corre- 

 sponding to the remarkable cell found at the apex of the main axis 

 and lateral branches of Splachnidium. In its reproduction it is allied 

 to the Laminariacece, and the production of sporangia within concep- 

 tacles might seem to point to a narrower limitation of the fertile sorus 

 of plants of this order, recalling the difference between perithecium and 

 apothecium in the fungi. 



