408 SUMMARY OF CURRENT RESEARCHES RELATING TO 



solely in the interest of the insect world ; though, so far, the facts barely 

 admit of any other interpretation. The author's view is that nature has 

 not made variety in structure and character solely for the peculiar 

 advantage of the plant itself, but that a variety of purposes are also 

 involved. 



Comparative Anatomy of the Bracts of the Involucre in Cichori- 

 aeese.* — M. L. Daniel describes the structure of the bracts in a number 

 of the CichoriacesB. In Tolpis harhata, for instance, in a bract from the 

 third row, the two hypodermal bands are formed by sclerenchymatous 

 parenchyme, and unite, completely enveloping the bundles. The struc- 

 ture found in the internal bracts is very different ; the lower band is 

 composed of two fibrous portions united by sclerenchymatous parenchyme, 

 beneath one or several bands of aqueous polyhedral parenchyme. The 

 author then goes on to describe numerous other genera belonging to the 

 Cichoriacese, and clearly shows that great variation in structure is to be 

 found within that tribe. 



Pitchers of Sarracenia-t — From an examination of the anatomical 

 structure of the pitcher of Sarracenia Drummondii, M. E. Heckel comes 

 to the conclusion that it represents a hollow petiole, and the opercule 

 the lamina of the leaf. The resemblance in structure is very close to 

 the petiole of Nymphsea alba, and the near affinity of the Nymph feacege 

 and Sarraceniacese cannot be doubted. The structure and arrangement 

 of the vascular bundles are very similar. The parenchyme of the petiole 

 of the water-lily contains large numbers of air-cavities lined with hairs. 

 These appear to be fused in Sarracenia into one large central cavity, the 

 cavity of the pitcher, in which we again find the hairs which prevent 

 the escape of the captured insects. 



Petiole of Dicotyledons.| — M. L. Petit describes the anatomy of the 

 petiole of nearly five hundred species of Dicotyledons belonging to three 

 hundred genera and forty-eight families. In form the petiole is always 

 convex below and concave on its upper face; the hairs present unim- 

 portant characters for classification, their existence not being constant in 

 the same family or genus. The external membrane of the epiderm is 

 generally 5 /a in thickness ; in Clerodendron foetidum and Cydanihera 

 pedata it is 3 /u, ; while in Eanunculacese it is sometimes 10 /x ; it is 

 nearly always more or less cuticularized. The form of the epidermal 

 cells is very variable, and their variations are independent of families or 

 genera. The presence of cork has been noticed in several cases, e. g. 

 Ficus repens, Theohroma Cacao, and Hoya carnosa. In the two former it 

 is in contact with the epiderm, but in Hoya carnosa it consists of five or 

 six layers, and is separated from the epiderm by four or five layers of 

 parenchyme. 



CoUenchyme is present in the petiole in two distinct forms ; some- 

 times the walls of the cells are thickened everywhere to the same extent, 

 as in UmbellifersD and many Eosaceae, while in other cases the thickening 

 is localized at the angles of the cells, as in Polygonacese. These two 

 types of collenchyme are connected by intermediate forms. The con- 

 junctive tissue is formed of round or polygonal cells with either thin or 



* Bull. Soc. Bot. France, xxxv. (1888) pp. 432-6. 

 t Comptes Rendus, cvii. (1888) pp. 1182-4. 



J Mem. Sci. Phys. et Nat. Bordeaux, iii. (1887) pp. 217-404 (6 pis.). Cf. this 

 Journal, 1888, p. 610. 



