1909] 



LEAVITT—HOMOEOSIS IN PLANTS 



47 



frond, as above described, 

 occupied bv pinnules much 



vard the extremity of the infertile 

 proximal fourth of this pinna is 



normal. This 



the pinna corresponding to the stipe of the frond, and would be bare 

 of pinnules were the frond-plan fully realized; as a matter of fact 



two form-forces are 

 expressed, the pin- 

 nar, which gives a 

 blade of proper 

 width on either side 



Fig. 10.— Normal pinna of Polystichum Braunii. 



of the mid- vein, and 

 the frondescent, 



which divides the blade. In the opposite basal pinna of this specimen 



pattern of the sterile frond. 



homoeosis refers to the terminal 



Gray. Near 



Herbarium 



interplay 



exhibits an interesting 



sight appears to be extreme irregularity gradually 



definite 



Pre-existing types. Frond-plan in the 

 Pinnae is expressed by 



segmentation 



the character of 

 the segments, by 

 their increased 

 le *gth, and 

 increased width 

 °* the distal two- 

 th irds, and in so 

 fr °m the low 



and by 



Fig. 11. — Homoeotic pinna of Polysti- 

 chum Braunii (specimen in herb. Gray). 



by the absence 



third G T er Side ° f the P innar rh achis, throughout the basal one 



or thereabouts of its length— in an "pfiWt" tn tmIiV.p thi 



length — in an "effort" to realize the 



segments, more 



Prolate condition of a frond 



ai "e thr ( "onu. x 11c segments, more or less complete, 



and th e S f °V he api . Cal region of the infertile frond of the s P ecies > 



form 



typ 



(P 



