DIVISION II 

 SPERMATOPHYTA 



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The Transition from the Pteridophyta to the Spermatophyta ( 1 ). 

 The Pteridophyta are characterised by the type of alternation of 

 generations they exhibit. The spore gives rise to the independently 

 living, haploid gametophyte. This is the short-lived prothallus, from 

 the fertilised egg -cell of which the physiologically independent 

 diploid sporophyte arises and forms the Fern, Horse-tail, or Club- 

 moss. The appearance of heterospory leads to a further reduction of 

 the prothallus, which ceases to produce both kinds of sexual organs. 

 In the germination of the microspores only a single, vegetative pro- 

 thallium-cell is to be recognised, the remainder of the small prothallium 

 representing one or more antheridia. The female prothallium, which 

 in Salvinia still becomes green and emerges from the macrospore, in 

 Selaginella and Isoetes has lost the power of independent nutrition. 

 The prothallium begins its development while still within the macro- 

 sporangium of the parent plant, and the macrospore, after being set 

 free, only opens in order to allow of the access of the spermatozoids 

 to the archegonia. From the fertilised egg the embryo develops 

 without a resting period into the young sporophyte. 



The simplest Spermatophyta are only distinguished by inessential 

 differences from these most highly differentiated Archegoniatae. 



The MACROSPORE, which in the Spermatophyta is termed the 

 EMBRYO-SAC, remains enclosed in the MACROSPORANGIUM or OVULE 

 (Fig. 508). The latter consists of the NUCELLUS (n), from the base of 

 which (the CHALAZA (ch)) one or two INTEGUMENTS (ii, ia) arise ; these 

 grow up as tubular investments of the nucellus and only leave a small 

 passage, the MiCROPYLE (m), leading to the tip of the latter. The 

 ovule is attached to the MACRO-SPOROPHYLL or CARPEL by a stalk or 

 FUNICULUS (/), which is often very short. The region to which one 

 or more ovules are attached is called the PLACENTA. If the nucellus 

 forms the direct continuation of the funiculus the ovule is termed 

 straight or ATROPOUS. More frequently the funiculus is sharply 

 curved just below the chalaza, so that the ovule is bent back alongside 

 its stalk (ANATROPOUS ovule). The line of junction of the funiculus 



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