IV. 



ON MALFORMATIONS OF ASCOPHYLLUM 

 AND DESMARESTIA. 



IN a short account of the galls in Rhodymenia palniata Grev., published 

 in the Journal of Botany for March, 1891, I referred to malformations 

 found in Ascophyllum nodosum which were shown me by Mr. George 

 Murray, having been collected by him at Stonehaven. During a visit 

 to Cumbrae last summer I found a number of Ascophyllum plants bearing 

 similar growths, and in one instance almost every branch of the thallus 

 was more or less affected. I collected specimens both from this plant 

 and from others near it, and preserved them for investigation in London 

 and for comparison with those I had already seen. 



The malformations are almost invariably confined to the part of the 

 thallus immediately above or below the air-vesicles, and in many cases 

 the thallus is broken away across the middle of a vesicle, the remaining 

 half being transformed into a solid mass of diseased tissue. On the 

 younger vesicles the swellings are considerably smaller than on those 

 nearer the base of the thallus, probably from having been more recently 

 attacked. The thallus in the affected parts is much swollen and covered 

 with small, round swellings or lumps, forming a corrugated surface 

 (plate VII., figs. I and 2) ; and a transverse section through this part 

 shows that each lump is a more or less hollow space containing numerous 

 nematode worms (plate VII., fig. 3). In the younger stages of the disease 

 the central part of the tissue is not affected, and the cavities are not 

 in communication with one another ; but in the older stages the whole 

 of the tissue of the affected part becomes diseased, and the partitions 

 between the cavities are broken down, both cavity and passage being 

 bordered by a thick wall of disorganized tissue closely pressed together. 

 The cavities are flask-shaped and have a small narrow opening at the 

 top, by which the nematodes appear to make their way in or out. In the 

 youngest stages of malformations that I have found, a slight rupture of 



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