Biological Papers. 77 



■leaf scars. Remarkable for their rich, palm-like appearance and for their 

 being a remnant of a class of plants that lived in great abundance and 

 vigor in Mesozoic times. 



Species 166. Cycas revoluta Thunberg. Cycad. A small tree (?), sel- 

 dom more than a meter high, usually much less, with a diameter of 20 to 

 30 centimeters. Raised in tubs, mainly in greenhouses, often in private 

 .houses. 



CLASS VII.* GINKGOINE.a:. GINKGOS. 

 Exogenous Fern-like Gymnosperms. 



Trees monoecious, with androspores and gynospores on the same tree. 

 Androphyls numerous, on small, ament-like, semipendulous racemes (andro- 

 phores) arising from a leaf-fascicle. Androsporangia (anthers) two, each 

 Tvith a single sporangium attached by one end, pendulous, and dehiscing by 

 a longitudinal slit. Androspores (pollen) tetrahedrally subspherical. Pol- 

 lination anemophilous. Carpophores compound, subpaniculate, not con- 

 spicuous, with about two naked ovules (gynosporangia) on a carpophyl at 

 the end of each branchlet; ovules provided with an embryo-sac (gynospore) ; 

 only one ovule usually fertilizes and develops, making a small edible nut. 



Order XII. GINKGOALES. The Maidenhair Trees. 

 Finely branching exogenous trees, with fascicled fern-like foliage. Trees 

 bear naked seeds on carpophyls at the ends of a compound carpophore. 



Family 27. Ginkgoace^. Maidenhair-tree Family. 



Stately trees, with numerous branches and branchlets, and with leaves 

 in scaly fascicles. Leaves annual (deciduous), petiolate, with the distal 

 portion gradually expanded into a fan-shaped lamina with dichotomous 

 radiating venation. Perifascicular scales opposite, obtuse, imbricate, in 

 four ranks. Fruit of the form and size of plums, with a hard pericarp, on 

 the tips of compound peduncles (carpophyls). 



Species 167. Ginkgo biloba Linnagus. (Salisburia adiantifolia J. E. 

 Smith.) Ginkgo; Maidenhair- tree. Occasional in cultivation, and grows 

 readily where the soil is not too thin and dry and the sunshine too intense. 

 A tree of Japan. 



Phylum *IV. STROBILOPHYTA. Strobilophytes. 



Cone-hearing Gyynnosperms. 



Carpels sometimes very minute; never form an ovulary. Ovules (gyno- 

 sporangia) in the axils of prominent scales upon a conspicuous strobile or 

 cone. Stigmas none. Anthers (androsporangia) spirally arranged on a 

 small fugacious ament (androphore), on the under side of each anther- 

 scale (androphyl), each anther carrying a single sporangium. 



In fecundation pollen (minute androspores carrying unciliated nonmotile 

 antherozoids or sperms) from an anther on a staminate ament falls directly 

 upon an uncovered ovule on a carpellate ament; the antherozo-ids enter the 

 micropyle (sacred entrance) of the ovule and fuse with the ovum within- 

 when shortly the carpellate ament becomes a cone or fuses into a small 

 berry. Pollination dependent upon the wind (anemophilous). The resulting 

 seed becomes covered and protected by the scale. Such a seed differs from 

 an oospore (part I, page 5) mainly in being more elaborate in structure, as 

 arising fro-n a fully developed archegonium. Purpose is the same— perpet- 

 uation of species; methods differ. 



