120 



The Scottish Naturalist. 



Phytoptus. In them the alterations in the inflorescences show 

 themselves only after some weeks, either in the development of 

 bracts or in the appearance of small, true leaves without axillary 

 flower-buds in the midst of the inflorescence, or in a slight degree 

 of doubling or proliferation in the flowers. If the infection was 

 carried out only once on a branch, then at the most only from one 

 to three successive flowers showed anomalies, or as many true 

 leaves appeared in the inflorescence ; the rest were normal. 



In the Cruciferre I obtained my results by laying several infected 

 buds of V. tripteris (of which a single one sufficed to ensure a 

 great degree of injury in Centranthus Calcitrapa) on the tip of one 

 and the same branch of the plant to be infected. The animals 

 crawl out as soon as the buds begin to wither and dry up, and 

 pass on to the living plant, upon which they move about, so that 

 one or the other cannot fail to gain access to the vegetative points. 

 To be more certain of this it is advisable to make infection of the 

 same plant at various times, in order to ensure that the susceptible 

 organ shall be reached and irritated by the animals, either at its 

 earliest origin, or in its earlier stages of growth. 



It may here be remarked that most infections of the 

 Valerianaceoe and of the other plants were made in spring, March, 

 and April, but in some species that flower in the end of June and 

 in July, they were made in May also. In July, August, and 

 September only a few infections were carried out ; in those species 

 that have been indicated as not favourable host-plants for Phy 'topi us 

 they produced no result except in Gochlearia officinalis, Brassica 

 nigra, Capsella Bursapastoris, Bellis perennis and Primula acaulis 

 which were infected in October, and were then cultivated indoors, 

 the two former in heat, the latter in a cool room. The Brassica 

 formed flower-buds, which remained very small, and did not open. 

 The small size of the flower-buds is a consequence not of the in- 

 fection but of cultivation in the dry air of a room. 



Since now on numerous Valerianaceoe and several Cruciferce, 

 abnormalities of structure have been artificially produced, by 

 means of one and the same species of Phytoptus, the question 

 pressed itself upon me whether similar abnormalities may not be 

 caused by other species of Phytoptus. I directed my attention to 

 a species that shows preference for the buds, and remains con- 

 stantly in them, or, to speak more correctly, remains in them until 

 the buds die. One has numerous individuals in a small space. 



