GYMNOS PERMS 431 



sporangium which produced it. This fact is referred to as 

 the retention of the megaspore. It needs to be borne in 

 mind. 



SPERMATOPHYTES 



We now come back to that great group of plants with 

 which we began. You are sure to find that what you have 

 learned concerning the lower groups of plants will help 

 you to a better understanding of this, the highest group. 



Seed plants fall naturally into two great divisions, gym- 

 nosperms and angiosperms. As you have already noted 

 (page 183) the fundamental difference between these groups 

 is that gymnosperms have their seeds exposed, while 

 angiosperms have their seeds inclosed. The seeds of 

 angiosperms are inclosed in that organ called the ovary. 

 Gymnosperms have no ovary. Gymnosperms evolved 

 before angiosperms, and they are simpler. We will con- 

 sider them first. 



79. Gymnosperms. (The word means naked seeds.} 

 Pines and other trees like them are the gymnosperms with 

 which you are familiar. You know that they have needle- 

 like leaves which stay on the year round, and for this reason 

 these plants are called evergreens. You know that they 

 produce cones, and that the seeds are in these cones. You 

 know that pine lumber is a soft, smooth wood which is 

 much used by carpenters. 



That division of gymnosperms to which pines and 

 forms like them belong is called Conifera. (The word 

 means cone bearers.} Besides the pines, the cedars, hemlock, 

 spruce, and arbor vitae also belong to the Conifers. 



Cones are aggregations of sporophylls ; that is, they are 



