292 FEKTILISATION EFFECTED BY MEANS OF INSECTS. 



upon the bracts of Conifers in the same light. In these cases there is 

 no evidence of the presence of a stigma. Gnet^cese seem to form a 

 link between Cycads and Conifers. They have an open ovary without 



l:> 



Fig. 518. 



style or stigma. The name of ArcMsperms (aj%>i, beginning, ffTTB^fia, 

 seed) has been given by some to Gymnospermous plants ; while the 

 term Metasperms {/iira, after) has been applied to Angiospermous 

 plants. These views will be noticed when 

 the natural orders are described. In treat- 

 ing of the embryogenic process it is probably 

 not of much importance which view we adopt. 

 The ovules of the so-caUed Gymnosperms (fig. 



520 ov, and fig. 521) consist of a nucleus (fig. 



521 a) covered by one or more integuments, 

 and having a large micropyle (fig. 520 mdc, and 

 fig. 521 m). In the delicate cellular nucleus 

 (fig. 521 a) there is developed an embryo- 

 sac, h, sometimes more than one, as in the 



Yew tribe. The poUen-grains enter the large micropyle and come 

 into contact with the nucleus, and then send their tubes into its apex 

 (fig. 522 c). This process sometimes requires several weeks or 

 months. After this the embryo-sac (fig. 522 b) becomes gradually 



Fig. 518. A Coniferotis tree, tlie Stone-pine, whicli belongs to the Gymnospermous divi- 

 sion of Phanerogams, the seeds being [naked, that is, not contained in an ovary with a 

 stigma. The seeds are in cones covered by scales. Fig. 519. A Cycadaceons plant (Cycas 

 revobuia), belonging also to the Gymnospermous division. The seeds in Cycads are produced 

 on the edge of abnormal leaves or on the lower side of scales of cones. Fig. 520. Female 

 flower of a Pine, consisting of a scale, eca, and two ovules, ov, attached to its base ; mw, the 

 foramen of the ovule. The ovules are nailed, not being contained in a true ovary. 



Pig. 620. 



