52 PROCREDINGS OF THE AMERICAN ACADEMY 



parts, and then after some growth one of these four cells had divided 

 au^ain into two, — a process which the other cells were probably about to 

 undergo. There is little to be ?aid regarding this ; what nourishment 

 the young frond reijun-ed to carry on ihe growth was probably taken 

 from the organic material in wliich it was buried. No giowth had 

 yet penetrated the cells of the Polysiphonia. 



The next stage that was observed in the development of the 

 frond was rather more complicated. The young frond was here 

 composed of a considerable number of cells, which, however, pre- 

 sented as yet no very detinite arrangement (Fig. 3). The gelat- 

 moOs intercellular substance was present to some extent, and a 

 touo-her layer of it already covered the outside surface. The first 

 indications of the growth of the parasite into the Polysiphonia were 

 also seen here. lu the figure (Fig- 3) where this stage is shown, two 

 cells will be seen that have thrust themselves between the cells of the 

 host plant, and have grown some little distance inwards. Even as early 

 as this the young frond of Choreocolax must have obtained some nour- 

 ishment from the Polysiphonia, or it would not have given evidence of 

 60 much activity of growth. Other than this there is no differentiation 

 in the cells of the frond ; the characteristic ariangement of the ter- 

 minal layer that is developed in the adult frond has not yet made its 

 appearance. Having once forced tlieir way into the tissue of the 

 Polysiphonia, the cells of the Choreocolax grow more rajiidly, and 

 finally come to encircle cells of the host plant. New filaments push 

 their way in, and grow in both directions, between the central and pe- 

 ripheral siphons of the Polysiphonia, attaching themselves chiefly to 

 the former. 



In the mean time the external portion of the frond has been in- 

 creasing in size. The cells which have pushed themselves into the 

 host plant have, besides fastening themselves to its cells, begun to 

 send out branches u^jwanls, which, by subsequent growth, are to form 

 a part of the external protuberance of the frond. As these cells in- 

 crease in number they press outwards, and, joining with the rapiilly 

 developing external portion {il ready .formed, displace the cells of the 

 host plant in the immediate neighborhood of this growth. Later, the 

 displaced cells of the Polysiphonia are entirely enveloped by the glow- 

 ing Choreocolax. No morbid growth is stimulated in them, however ; 

 they remain entirely passive, and are gradually absorbed by the para- 

 site, so that in adult specimens there is usually no trace of them left. 



Comparatively early in the development of the frond, before the 

 internal growth of the vegetative filaments has pushed aside the cells 



