ZOOLOGY AND BOTANY, MIOROSCOPYj ETO. 85 



— (1) The median vertical plane of the cotyledons always corresponds with 

 a vascular bundle in the root. (2) The bundles of the root never pass 

 the cotyledons. (3) The insertion of the cotyledonary bundles on the 

 bundles of the root follows a general principle. (4) There is no 

 absolute limit between the stem and the root. (5) The number of 

 bundles in the root corresponds in a certain measure with those of the 

 cotyledons. 



(4) Structure of Orgrans. 



' Dimorphism of the Flowers of the Horse-chestnut.* — Sig. U. 

 Martelli has observed two kinds of dimorphism in the flowers of 

 JEsculus Hippocastanum. One kind relates to the arrangement of the 

 patches of colour at the base of the petals, and appears to be related to 

 the visits of insects. In addition to this, the greater number of the 

 flowers in a spike are abortive, only a few being perfect. These fertile 

 floweBS are found only in the lower part of the inflorescence, and appear 

 there to be arranged in regular order. Similar observations were made 

 on some other species of the genus. 



Cleistogamous Flowers of Tephrosia heterantha.f— Herr G. Hiero- 

 nymus describes the structure and mode of fertilization of this plant 

 from the Argentine Republic. The cleistogamous flowers contain only 

 five stamens and two or three instead of the fifteen ovules in the open 

 flowers. The pollen-grains are few in number, and their pollen-tubes 

 pierce the wall of the anther in order to reach the stigma. 



Hermaphroditism of Lychnis dioica when attacked by ITstilago.l — 

 M. A. Magnin points out that the flowers of Lychnis dioica L. (L. ves- 

 pertina Sibthrp.) are ordinarily unisexual ; Linnaeus, however, determined 

 the possibility of hermaphroditism, and M. Crie has called attention to 

 the floral polymorphism of this plant. The author states that Lychnis 

 dioica is often attacked by Ustilago antherarum, and that the effects pro- 

 duced are different according to the sex that is attacked. In the male 

 it only causes a slight malformation of the anthers, and the replace- 

 ment of the pollen by the spores of the Ustilago, while in the female it 

 causes the appearance of stamens ; the female organs undergo partial 

 atrophy, while the plant retains otherwise altogether the characters of 

 the female plant in habit, mode of branching, &c. 



Zygomorphy and its Causes.§ — Mr. C. Eobertson discusses the 

 causes of zygomorphy in flowers, especially in relation to the mode of 

 pollination by insects, whether the flower is nototribal, sternotribal, or 

 pleurotribal, in Delpino's use of these terms, i. e. whether the pollen 

 from the open anthers is deposited on the back, the abdomen and leos 

 or the side of the visiting insect. Mr. Eobertson holds that the first 

 change towards zygomorphy is for the stamens and styles to turn 

 down at the bases and up at the tips, so as to strike the under side of 

 the insect more effectually ; the lower nectaries, being thus rendered 

 less accessible, will tend to abort. Irregular polypetalous flowers are, 

 as a rule, sternotribal ; some, however, are nototribal, as most orchids, 



* Nuov. Giorn. Bot. Ital., xx. (1888) pp. 401-4. 



t JB. Schles. Gesell. Vaterl. Cultur, 1887, pp. 235-8. See Bot. Centralbl., xxxvi. 

 (1888) p. 170. X Comptes Rendus, cvii. (1888) pp. 663-5, 876-8 



§ Bot. Gazette, xiii. (1888) pp. 146-51, 203-8, 224-30 (2 figs.). Cf. this Journal, 

 1887, p. 779. 



