35i PLA^^T STUDIES 



the intra-seminal develojoment. In this condition the em- 

 bryo may continue for a very long time, and it is a ques- 

 tion whether it is death or suspended animation. Is a 

 seed alive ? is not an easy question to answer, for it may 

 be kept in a dried-out condition for years, and then when 

 placed in suitable conditions awaken and put forth a liv- 

 ing plant. 



This " awakening " of the seed is spoken of as its " ger- 

 mination," but this must not be confused with the germi- 

 nation of a spore, which is real germination. In the case 

 of the seed an oospore has germinated and formed an em- 

 bryo, which stops growing for a time, and then resumes it. 

 This resumption of growth is not germination, but is what 

 happens when a seed is said to " germinate." This second 

 period of development is known as the extra-seminal^ for it 

 is inaugurated by the escape of the sporophyte from the 

 seed coats (Fig. 315). 



234. The great groups of Gymnosperms. — There are at 

 least four living groups of Gymnosperms, and two or three 

 extinct ones. The groups differ so widely from one an- 

 other in habit as to show that Gymnosperms can be very 

 much diversified. They are all woody forms, but they may 

 be trailing or strangling shrubs, gigantic trees, or high- 

 climbing vines ; and their leaves may be needle-like, broad, 

 or " fern-like." For our purpose it will be only necessary 

 to define the two most prominent groups. 



235. Cycads. — Cycads are tropical, fern-like forms, with 

 large branched (compound) leaves. The stem is either a 

 columnar shaft crowned with a rosette of great branching 

 leaves, with the general habit of tree-ferns and palms (Figs. 

 16, 316) ; or they are like great tubers, crowned in the 

 same way. In ancient times (the Mesozoic) they were very 

 abundant, forming a conspicuous feature of the vegeta- 

 tion, but now they are represented only by about eighty 

 forms scattered through both the oriental and occidental 

 tropics. 



