86 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Viola, and Impatiens. Orchids must have developed as sternotribal, and 

 become nototribal by the twisting of the ovary. The following is a 

 summary of the general conclusions at which Mr. Eobertson has 

 arrived. 



When shallow flowers become horizontal, insects light on the stamens 

 and styles, and prefer the upper nectary. The stamens and styles bead 

 to the lower side, and the lower nectaries abort, Zygomorphic flowers 

 of shallow origin are sternotribal, and have a single nectary, or a central 

 nectary more strongly developed or more accessible on the upper side. 

 Nototribal flowers of shallow origin are inverted. When regular 

 tubular flowers with included stamens and styles become horizontal, 

 insects land on the lower border and prefer the lower nectary. The 

 stamens and styles bend to the upper side, and the upper nectaries abort. 

 Zygomorphic flowers of deep gamopetalous origin are nototribal, and 

 have a single nectary, or a central nectary more strongly developed or 

 only accessible on the lower side. Sternotribal flowers of deep gamo- 

 petalous origin have originally exserted stamens and styles, or have 

 become shallow. Irregular flowers were modified with reference to a 

 landing-place, and were modified through the influence of insects light- 

 ing uj)on them. Irregular flowers adupted to insects which do not light 

 have changed visitors. Small closely-crowded flowers do not tend to 

 become zygomorphic. Small closely- crowded irregular flowers are 

 liable to lose their zygomorphic characters, unless the stamens and 

 styles are protected by galeas, carinse, &c. 



Opening of the Anthers of Cycadese.* — Of the different modes in 

 which, according to Herr J. Schrodt, anthers and sporanges open in 

 order to allow of the escape of the pollen and spores respectively, the 

 anthers of Cycadeee belong to the class in which there is no " fibrous 

 layer " in the wall, the mechanism of the rupture being due to other 

 causes. From the examination of a number of species of Zamia, Gerato- 

 zamia, Stangeria, Oycas, Encejphalartus, &c., Herr Schrodt arrives at 

 the conclusion that the epidermal cells of the anther-wall contain, in 

 their membrane, a substance which varies according to the species, and 

 which, when in contact with water, swells up more strongly than the 

 cell-wall which incloses it, so that the latter is placed in a state of 

 tension. Of the three layers of cells of which the anther-wall of Cycadese 

 is composed, it is only the epiderm which takes any part in the opening 

 and closing of the valves. The epiderm consists of cells elongated 

 in a direction parallel to the longitudinal axis, which contain within 

 their walls masses of cellulose capable of great expansion and contraction, 

 and whose thick lignified inner membrane offers greater resistance to the 

 contraction which results from desiccation than the thinner cuticularized 

 outer membrane. 



Protection of Buds in the Tropics.f — Herr M. Treub describes the 

 contrivances by which, in many cases, leaf-buds and flower-buds are 

 protected against excessive insolation in the Tropics, Among the most 

 interesting is that of Spaihodea campanulata (BignoniacesB), a tree of 

 Tropical Africa, in which the inflorescence is umbrella-shaped, and the 

 flowers completely exposed to the rays of the sun. The buds have the 



* Flora, Ixxi. (1S88) pp. 440-50 (1 pL). Cf. this Journal, 1886, p. 828, 

 t Handel. Nederl. Nat. en Geneesk. Congres, Sept. 30, 1887, p. 130. See Bot. 

 Centralbl., xxxv. (1888) p. 328. 



