GYMNOSPERMS 



211 



FIG. 201. Two views of the sperm of a cycad, 

 showing its spiral form and many cilia. 



of large compound leaves, with the general habit of tree- 

 ferns and palms (Figs. 198 and 199); or they are like great 

 tubers, crowned in the same way (Fig. 200). The tuberous 

 stems are often more or less buried, as in our only cycad 

 from the United States 

 (Florida), illustrated in 

 Fig. 200. In ancient 

 times cycads were 

 very abundant, but 

 now they are rep- 

 resented by about 

 eighty species scat- 

 tered through the ori- 

 ental and occidental 



tropics. They are especially interesting in their resem- 

 blances to ferns, and some of them might be mistaken for 

 ferns did they not bear large seeds. In addition to their 

 fern-like leaves, they have in the structure of the stem 

 many fern characters; and they have coiled sperms with 

 many cilia (Fig. 201), as do the ferns. They are very 

 interesting to study; but it is easier to obtain the Gym- 

 nosperm characters from the other group, whose forms are 

 far more familiar and easily obtained. 



Conifers are the common Gymnosperms, often forming 

 great forests in temperate regions. Some of the forms are 

 widely distributed, as the pines; while some are now very 

 much restricted, as the gigantic redwoods (Sequoia) of the 

 Pacific slope. The habit of the body is quite characteristic, 

 a central shaft extending to the very top (Fig. 42). In 

 many cases, the branches spread horizontally, with dimin- 

 ishing length to the top, forming a conical outline, as in the 

 firs. This habit gives the conifers an appearance very 

 distinct from that of the other trees. 



Another peculiar feature is the needle-leaf. These leaves 

 have a small surface and very heavy protecting cells, being 



