PHYLLO- 



57 



Phyllarthron DC. Bignoniaceae (4). 6 Madag. , Mascarenes. The 

 1. is reduced to a jointed winged petiole. 



Phyllepidum Rafin. Amarantaceae (inc. sed.). Gen. dubium. i 

 N. Am. 



Phyllis L. Rubiaceae (n. 7). i Canaries, Madeira. 



Phyllitis Ludwig. Polypodiaceae. 10 trop. and subtrop. 



Phyllo- (Gr. pref.), -phyllous (suff. ), leaf; -clade, a stem structure 

 usu. flattened and serving 1. purposes, Asparagus, Baccharis, Bos- 

 siaea, Carmichaelia, ffibbertia, Lathyrus, Leinna, Miiehlenbeckia, 

 Oxalis, Phyllanthus, Phyllocladns, RHSCHS, Semele; -de, a petiole 

 flattened and green, taking over 1. -functions, Acacia, Oxalis; -dy, 

 change of fl. organs to 1. ; -me, a leaf structure; -taxy, the arrange- 

 ment of the 1. upon the stem. It follows definite rules, esp. in 

 flowering-plants, though it varies within certain narrow limits. The 

 1. may be several at each node (in whorls), or two (usu. opposite), 

 or one (alternate). When the stem is so short that the 1., as in the 

 primrose or dandelion, are all crowded together and spring from the 

 level of the ground, they are said to be ' radical. ' In the first two 

 cases the I. at one node usu. stand above the gaps at the node below. 

 In the case of alt. 1. there is found to be a fairly constant angle 

 between each 1. and the next one above it, e.g. in Plantago (fig.) this 

 angle is f of the whole circumference measured the nearest way. 

 This fraction f represents 

 the phyllotaxy. Twist- 

 ing excepted the 1. will 

 stand in 8 vertical rows, 

 each divided from the 

 next by \ of the circum- 

 ference. Leaf 2 will be 

 f , 3 will be f , 4 will be 

 f, 5 will be V-> 6 will be 

 Y-, 7 will be V, 8 will 

 be -V~> an d 9 will be -\ 4 -, 

 of the circumference from 

 leaf i, i.e. immediately 

 over it, and three turns of 

 the spiral aboveit. Hence 

 the rule for determining 

 phyllotaxy: start from any 

 1. A and draw a spiral 

 round the stem, passing by 

 the nearest way through 

 all consecutive 1. to the 1. B exactly above A; then the number of 1. 

 from A to B is the denominator, the number of turns of the spiral 

 the numerator, of the fraction representing the phyllotaxy. 



In Gramineae the phyllotaxy is 5, i.e. alt. on opp. sides of the 

 stem, in Cyperaceae \. Nearly all other actual arrangements are 

 terms of the continued fraction starting from |, g. If we add the 

 numerators together to make a new numerator, and treat the denomi- 

 nators in the same way, we get the next arrangement f . This with 

 \ gives f , and then fa and so on. It is rare to find a stem that shows 



PHYLLOTAXY. 



