Miscellaneous. 353 



this opinion. He declares himself also against the opinion which 

 derives all the parts of the stem from a single layer of cambium 

 existing in the terminal bud. According to him, the entire terminal 

 bud is formed of cambium, and already contains the mother cells of 

 all the kinds of tissue which will subsequently form the various parts 

 of the stem. — Jahrb.fiir Wiss. Bot. 1864; Bibl. Univ. 1865, Bull. 

 Sci. p. 87. 



Graduation from "Individual Peculiarities " to Species in Insects. 



The following are the concluding paragraphs of a paper by Dr. B. 

 D. Walsh " On Phytophagic Varieties and Phytophagic Species." 

 The name phytophagic is given to those otherwise identical insects 

 which differ, as varieties or species, according to the species of plant 

 they feed upon. " When certain unimportant characters in the 

 insect are correlated with the food-plant, while at the same time there 

 is no sufficient reason to doubt that the two varieties freely inter- 

 cross," the forms are called phytophagic varieties. When, from the 

 lack of intermediate forms, intercrossing may be inferred not to take 

 place, they are called phytophagic species. Dr. Walsh sums up his 

 conclusions thus : — 



" From the facts referred to above, and those recorded by me else- 

 where, we may construct the following almost unbroken series, from 

 the first dawnings of the Phytophagic Variety to the full develop- 

 ment of the Phytophagic Species : — 



" 1st. Difference of food, even when the food-plant belongs to 

 widely distinct botanical families, is accompanied by no difference 

 whatever either in the larva, pupa, or imago state : Attacus Cecropia, 

 Linn. ; Dryocampa imperialis, Drury ; Lachnus Caryce, Harris 

 (Proc. Ent. Soc. Phil. vol. i. p. 303) ; and hundreds of other species. 



" 2nd. Difference of food is accompanied by a marked difference 

 in the colour of the silk-producing secretions : Bombyx Mori, Linn., 

 the common silkworm. 



" 3rd. Difference of food is accompanied by a tendency toward the 

 obliteration of the normal dark markings in the imago : Haltica 

 alternata, Illig. 



" 4th. Difference of food is accompanied by marked, but not per- 

 fectly constant, colorational differences in the larva, but none what- 

 ever in the c? $ imago : Datana Ministra, Drury. 



" 5th. Difference of food is accompanied by a marked and perfectly 

 constant difference in the size of the imago : Chrysomela scalaris, Lee. 



"6th. Difference of food is accompanied by a marked difference 

 in the chemical properties of gall- producing secretions, the external 

 characters of the 6 $ imago remaining identical : Cynips q. spon- 

 gijica, O. S., and C. q. inanis, O. S. 



" 7th. Difference of food is accompanied by a slight but constant 

 change in the coloration of the abdomen of the d $ imago, and by 

 a very slight change in the chemical properties of the gall-producing 

 secretions, the galls of the two insects, though typically somewhat 

 distinct, being connected by intermediate grades in the case of the 

 latter : Cynips q. punctata, Basset, and C. q. Podagrce, Walsh. 



