284 Al'IIELEXCIIUS I'lIYLLOPIIAGUS IN CIIHYSAXTIIKMUMS. 



of the profound nietanioipliosis undergone during its life-cycle, 

 and TylciicUus differs from Aphclciichus in that the male possesses 

 an inconspicuous " bursa copulatrix." Apliclenchus, in common 

 with tlie two other genera, is provided with a chitinous boring 

 organ or " sjjear " whereby the jiarasite is able to penetrate the 

 tissues of the host plant. .1. pJnjtloiituKjus, as the name indicates, 

 is pai'asitic on the leaves. Very occasionally it may be found 

 located in other parts of the j^lant. The present author found 

 only one or two individuals in the parenchyma of the stem of 

 an old, severely-infested plant. This, however, appears to be 

 abnormal, and in our case was possibly accidental. 



The route whereby the j)arasite reaches its definitive liabitat. 

 as recorded by [Stewart, is by making its way up the surface of 

 the stem of the plant into the leaf axils, where, incidentally, the 

 female may deposit her eggs. The eggs on hatching produce 

 relatively thin, small larvae, which creep on to the under-surface 

 of the leaves and invade the mesophyll via the leaf stomata. 

 Soon after infection (about one week) the leaf becomes marked 

 by a brown area, which increases in size vmtii eventually the leaf 

 wilts and falls from the plant. The parasites nuiltiply rapidly 

 in the leaf, and a, severely-infected leaf may contain as many as 

 sixty individuals in all pliases of development. 



Control. 



From personal examinations of the soil it was only occasion- 

 ally that I found a few specimens of the parasite. Usually there 

 were only four or five individuals which could be positively 

 identified as Aplicloicliitx, found in small wa.tch-glass sainples 

 of soil taken from pots with infested plants. Those few found 

 w^ere larvae, that only revived after some considerable time in 

 water. On the other hand, leaves, which had fallen from the 

 plants and had remained on the ground for as long as three 

 months, were found to contain large numbem of the parasites that 

 speedily revived after immersion in water. 



The leaf, theii, must be regarded as the reservoir of the 

 parasite during the winter period. The infected leaves should, 

 therefore, be systematically destroyed by burning. This should 

 constitute the chief prophylactic measiu'e to be employed in com- 

 bating the disease, as, when neglected, the leaves may fall near 

 the dormant stool of the plant and act as the centre of infection. 

 Leaves on the growing plant might also be removed i^rofitably 

 as soon as infection becomes evident. 



Chemicals as a !Means of Control. 



Stewart, on the authority of Mangin (1805), states that it is 

 only in the case of plants such as Everlasting, where the flowers 

 are stored in w'arehouses, that chemical treatment is of any use. 

 " Exposure to a dry atmosphere saturated with ca,rbon bisulphide 

 for 24 to 48 hours kills the parasites without affecting the appear- 



