THE ORGANS OF THE GROWI.\ 7 G FERN. g 



the under surface is covered with a white or yellow powder 

 bearing some resemblance to flour or corn starch. For this 

 reason a surface of this character is called farinaceous. Such is 

 the California gold-fern or "golden back" (Gymnogramme trian- 

 ^i(laris), and several of the cloak-ferns (Notholcend), and such 

 are the various gold and silver ferns of conservatories, including 

 some of the richest arid most beautiful in the world. 



23. The frond may be simple, when it consists of a single 

 undivided leaf, as in Scolopendrium or Camptosorus ; or compound, 

 when it is divided into segments. The exquisite delicacy and 

 the extent to which this dividing is carried in some ferns deter- 

 mines largely their aesthetic value. 



The continuation of the stipe through a simple frond is'called 

 the midvein ; through a compound frond is called the rachis, 

 and is further distinguished as primary when the frond is much 

 compounded. A frond is entire when the margin forms an 

 unbroken line; when so cut as to form lobes extending half 

 way or more to the midvein it is called pinnatifid ; when these 

 incisions extend fully to the midvein the frond is said to be 

 simply pinnate, and the divisions are called pinna. When the 

 pinnae are cut into lobes the frond is bipinnatifid and the lobes 

 are called segments, and when these extend to the secondary 

 midveins it is bipinnate and the divisions are called pinnules. 

 The secondary midvein then becomes a secondary rachis. In 

 like manner we may have ferns that are tripinnatifid and tripin- 

 nate, quadripinnatifid and quadripinnate. The last lobes are 

 designated ultimate segments, and the last complete divisions 

 ultimate pinnules. All these various forms from entire to quad- 

 ripinnate are abundantly represented among our native ferns. 



24. In some pinnate fronds, as in the oak-fern (Phegopteris 

 dryopteris), the lower pair of pinnae is greatly enlarged and 

 more compound than those above, so that the stipe appears to 

 form three branches bearing similar and nearly equal portions. 

 Fronds of this character are usually triangular or pentagonal in 

 outline, and this method of branching is called ternate. It will 

 be readily seen that this is merely a modified form of the ordi- 

 nary pinnate frond. Throughout the domain of nature there is 

 infinite variety of form and structure, and at the same time unity 

 in plan and conformity to a few generalized types. 



