PLATE I— CYCADE.E. 



(Cycas and Zamiaj'rom Dodtl-Port and Luerssen.) 



Cycads belong to the warmer parts of the world, their chief centres being Tropical America, South Africa, Eastern Asia, and Australia. 

 Although there are no living representatives in this country, still as they form the base of the lowest class of Phanerogams, or seed- 

 bearing plants, they naturally come in first for consideration. 



They show the nakedness of the seeds, or Gymnospermy, and the leafy nature of the ovule-bearing organs so clearly, that they are 

 referred to in the most elementary text-books of Botany, and this also must be taken as some sort of justification for introducing them 

 here. 



The practical examination of the Coniferae, with which they are closely allied, will enable the student to understand the various 

 drawings, where he cannot hope to obtain specimens. Cycads may be seen growing in the " Palm-houses " of our Botanic Gardens, 

 where their resemblance to Tree-ferns, or Palms, is strikingly manifest. 



The genus Cycas shows, in a very elementary form, the essential characteristic of the Phanerogams, viz. the structure of a Flower 

 producing Seed The terminal bud of the stem becomes a flower of the simplest kind — a number of modified leaves arranged spirally 

 on an axis, and these modified or carpellary leaves assume the simplest form — their lobes being converted into naked ovules. The 

 central bud of the flower again grows out and produces ordinary leaves, thus showing the flower to be a modified bud, and the carpels or 

 ovule-bearing organs to be modified leaves. 



Fossil forms are found in this country, particularly in the Upper Oolite. In the Island of Portland there are the remains of an old 

 land surface, known as the " Dirt Bed," and in it are embedded the roots and woody stumps of Cycads. 



General Characters — 



Fig. 1. In Cycas the male and female flowers are produced by distinct individuals, but both plants have the same general aspect 

 Stem, woody, fifteen to twenty feet in height, surface covered with the scars of fallen leaves, and summit bearing 



a terminal crown of leaves, in the centre of which is the terminal bud. 

 Leaves, of three kinds — scale-like leaves, foliage leaves, and carpellary leaves. 

 Scale-leaves envelope the bud, while a new crown of foliage-leaves is being prepared, and thus alternate regularly 



with them. 

 Foliage-leaves are pinnate, and form a palm-like crown. 

 Carpellary leaves produced by the terminal bud, and bearing ovules. 



Flower — 



Figs. 2 and 3. The leafy nature of the carpel shown. 



The Carpellary leaf in Cycas bears a general resemblance to the ordinary foliage-leaf, but is smaller, and may be 



either lobed (Fig. 2) or pinnate (Fig. 3). The lower portion of the leaf is fertile, bearing ovules instead of lobes or 



pinnae. 



Fig. 4. Mature Ovule about the size of a plum and like it, with a soft outer and a hard inner portion. 



Fig. 5. Male Flower of Zamia a cone, consisting of an elongated axis, covered with a number of scales, bearing pollen-sacs. 



Fig. 6. Transverse and longitudinal section of flower of Cerato-zamia. 



Scales arranged radially on a central axis, and bearing pollen-sacs on their under surface. 

 Fibro-vascular bundles pass out to each scale from the axis. 



Fig. 7. Stamen of Zamia shield-shaped. 



Fig. 8. Female flower of Zamia a cone, consisting of an elongated axis with scales closely packed, and their thickened ends 



hexagonal in shape. 

 Fig. 9. Carpel in the form of a scale, bearing two ovules on the under surface. 

 Seed — 



Fig. 10. Mature Ovule, before pollination. 



(a.) Outer succulent coat removed. End of shell perforated where the fibro-vascular bundles passed through. 

 (b.) Vertical section. 



Outer shell. 



Fibrous sheath representing remains of Nucellus. 



Primary Embryo-sac 



Secondary Embryo-sacs. 

 Fig. 11. Seed of C. circinalis in vertical section. 



Outer succulent layer. 



Inner hard layer. 



Endosperm. 



Embryo with two Cotyledons. 



In addition to the perfect Embryo there are several rudimentary Embryos. 



CLASSIFICATION. 



Sub-kingdom. — Phanerogams, so-called because the reproductive organs are generally more conspicuous than in Cryptogams. 

 Reproductive organs condensed into conspicuous structures known as Flowers. 



Seed produced from the flower, and containing an embryo before it is detached from the parent plant. 

 Group. — Gymnosperms. 



Ovules not enclosed in an ovary. 



Embryo-sac with endosperm before fertilisation. 



Pollen-grain divided into two or more cells. 

 Order. — Cycadeae. 



Stem, seldom branched. 



Foliage-leaves, large and usually pinnate. 



Flowers, in the form of cones, or as a rosette of leaves. 



Male and Female Flowers produced on different individuals. 



Ovules on the margins of carpellary leaves or scales. 



