﻿18 The Nciv York State College of Forestry 



insure a wider dissemination. Sexuality is a necessary part of the 

 life cycle and is insured through the transfer of male elements 

 to the proximity of the female nuclei by means of pollen grains. 

 Following the union of the sex nuclei a young sporophyte or 

 embryo is formed within the o\'ule or developing seed which, as 

 the latter matures, passes into a dormant condition. Upon subse- 

 quent germination of the seed, the young sporophyte again assumes 

 an active existence. 



The Spermatophytes in turn are divided into two classes, the 

 Gymnosperms and the Angiosperms, which are distinguished by 

 the manner in which the seeds are borne. The word gymnosperm 

 is derived from the Greek yofjyor, meaning naked, and T-e/t/m seed, 

 and includes those Spermatophytes in which the seeds are not 

 enclosed in an ovary but are borne naked, subtended by scales 

 or fleshy structures. Angiosperm comes from the Greek ayYe'tov, 

 meaning vessel, and ffTT^ptm seed, and embraces those forms in 

 which the seeds are borne enclosed in an ovary which may or may 

 not dehisce at maturity. The boundary between the two groups is 

 sutiiciently clear to serve the purposes of classification although 

 it in no way indicates the disparity in numbers and size. 



Gymnosperms are very ancient and form but a small part 

 of the present seed-plant vegetation. Some 450 living forms exist 

 today which are to be regarded as the surviving remnant of a 

 vast phyllum which had its genesis in the Carboniferous and 

 flourished during the Triassic. Angiosperms were evolved com- 

 paratively recently (lower Cretaceous) in a geological sense and 

 now are represented by a vast assemblage of approximately 125,000 

 species which comprise the bulk of the seed-plant vegetation of 

 the present day. They have been able to attain and hold the 

 ascendancy over the other groups because of adaptive features 

 which they have developed to meet the environmental conditions 

 in force at the present time. The chief superficial characters 

 which separate the group from the Gymnosperms are the presence 

 of the flower with its showy perianth, stamens and pistil and the 

 manner in which the ovules or immature seeds are borne enclosed 

 in an ovary. 



Two sub-classes of Angiosperms are recognized, the Monocoty- 

 ledons and the Dicotyledons, which are characterized as follows : 



(a) Monocotyledons possess but one seed leaf or cotyledon 

 which is terminal on the axis ; dicotyledons possess two seed leaves 

 which are lateral. 



