Jury, r915.] THE ORCHID REVIEW. 1y9° 
female gametes, thus securing cross-fertilisation between separate 
individuals, and that sexual zoospores are no longer produced. 
The Vasculares, including the ferns, lycopods and horse-tails, show an 
enormous advance in the asexual generation, which is analogous to the moss- 
fruit, and which has now attained a complexity almost rivalling that of the 
flowering plants, while the sexual generation has receded to a small 
membranous prothallus, which bears the sexual cells in antheridia and 
archegonia, as in the Bryophyta. The two generations have practically 
reversed themselves, for the fern plant, to use a familiar term, is not the 
equivalent of the moss plant, while the elaborate system of vascular tissue 
in the former is an entirely new development, which intervenes between the 
germination of the fertilised ovum and the production of the asexual spores. 
The sporophyte in this group is greatly diversified, while in some cases it 
bears two kinds of spores, microspores, forming numerous small prothalli,. 
and macrospores, forming a few large prothalli, on which the male and 
female cells respectively are borne. The vascular system is only developed 
in the sporophyte: 
Among the Gymnosperme—cycads and conifers—there is no longer an 
alternation of generations, for the female odphyte has lost its independence 
altogether. It never leaves the megaspore, which itself remains shut up 
within the tissues of the sporogonium.' Fertilisation now results tn the - 
production of a new body, called the fruit, consisting of the fertilised:ovum 
and its protecting envelopes. The ovum matures into the seed, from which 
the new individual is developed. The male fertilising organs are the pollen 
grains, which are here multicellular, and are produced within the anther. 
The sexes are separate, and the flowers are produced in the axils of 
protecting scales, but are destitute of a perianth, while the ovules are not 
contained within an ovary. Fertilisation in this group is a slow and 
complicated process, and it will suffice to say that the pollen grains are 
wind-borne, and on reaching the ovules develop a pollen tube, which 
penetrates the endosperm—a mass of nutritive tissue which fills the 
embryo-sac (the latter representing the megaspore of the higher 
Cryptogams)—and enters the micropyle of the ovule, after which the 
nuclei of the pollen and ovule fuse together, and then develop into the 
seed. Fertilisation by pollen tube marks the beginning of the flowering 
plants, or Phanerogams, but it is noteworthy that in a few primitive 
Gymnosperms the earlier method by motile spermatozoids is partly 
retained, the pollen tube being first formed, but afterwards liberating two- 
ciliated spermatozoids, which complete the work of fertilisation. The 
process marks an interesting transition between the higher Cryptogams. 
and the Phanerogams. 
In the Angiosperme the ovules are contained within a closed ovary, 
