MR JOHN RATTRAY ON ECTOCARPTJS. 595 



pores, the one being directed towards the base of the filament, the other towards 

 its apex (fig. 8, a), or both being placed approximately at right angles to its axis, 

 either on opposite sides (fig. 8, c), or on the same side, at other times by three 

 apertures arranged in various ways (figs. 11, a, and 12). It should here be 

 noted that these apertures in the cell wall of the parasite often lie in different 

 planes, and that it is not always possible to see all of them without a change of 

 focus under the microscope. 



Although two or three openings are of frequent occurrence in the cell 

 membrane of the parasite, the cell wall of the host plant invariably opens only 

 at one point, and in many cases it is possible to see clearly the margins of the 

 ruptured wall (figs. 7, 9, 1.0, and 11). It may also be observed, that this ovoid 

 wall is no longer able to recover its original form after rupture, inasmuch 

 as the limit of its elasticity has in most cases been passed, so that a perfect 

 rebound is not possible, while the long continued internal tension has con- 

 tributed to it a certain fixity of form which its remaining elasticity is not able 

 to reverse. 



In some cases (fig. 9) one meets with a remarkable involution of the wall of 

 the host cell after rupture has occurred. This fold, which usually occupies a 

 position approximately diametrically opposite to the place of rupture, may have 

 resulted either from the fact that the cellulose wall burst before the limit of its 

 elasticity was passed, so that a sudden and sharp recoil became possible, or 

 from the impact of some foreign body which, by striking against the involuted 

 region, at once caused that fold, and affected a rupture of the wall at the 

 diametrically opposite point. The occurrence of such a fold is, however, un- 

 usual. 



After rupture the swollen cell membrane of the parasite, which invariably 

 remains very thin and pliable, exhibits numerous creases, which become especi- 

 ally manifest when examined under a water immersion high power lens (fig. 7). 

 These fine irregular folds point to the presence of a certain amount of rigidity 

 in this membrane, which may be partly induced by direct contact with the 

 water of the surrounding medium. That the immense surface which the intact 

 but swollen host-cell membrane offers to the waves must tend powerfully to bring 

 about the complete destruction of the host plant by inducing or effecting complete 

 breakages of the thallus at these already weakened regions is at once obvious. 



When the parasitic cells have just opened, relief from internal tension is at 

 first experienced in the neighbourhood of the orifice or orifices, and it is often 

 possible to observe that the young swarmspores, into which the protoplasm has 

 divided, and which lie toward the opposite side of the cell, have, at this time, an 

 angulated or polyhedral outline. This, however, is of a transitory character, and 

 is due to the mutual pressure resulting from their continued growth (fig. 11, a). 



A peculiar and interesting disposition of the swarmspores is to be observed 



