356 Trcmsactions. — Botany. 



insect has been modified to suit the relative size of the species by which the 

 plant is fertilized, for if the passage had been of a size sufficient to allow the 

 largest individuals to escape with ease the smaller ones would perhaps have 

 been able to pass through without touching the rostellum. and consequently 

 would not remove the pollinia. 



It seldom happens that all the pollinia are removed. Out of 110 withered 

 flowers twenty-eight had all the pollinia remaining in their anther cells, 

 twenty-nine had lost one, thirty-four two, thirteen had three withdrawn, while 

 only six had all four removed. Seventy-one of the flowers were fertilized, but 

 it must not be forgotten that a large number of the unfertilized ones drop ofi* 

 before commencing to wither, so that the proportion fertilized is really much 

 less than this. Probably not one quarter of the flowers ever produce 

 capsules. 



Of the other species of Pterostylis, P. hanJcsii, P. graminea, and P. 

 puherula are fertilized in exactly the same manner. There are, of course, 

 slight diflerences in the size and arrangement of the parts of the flower, but it 

 is hardly worth while describing these in detail here. In P. 'puherula nectar 

 appears to be often present on the outside of the lateral sepals, near the point 

 of their coalescence, serving, no doubt, to attract insects to the flower. 

 P. hanksii also has two minute papillae at the base of the column, which may 

 secrete nectar, but I have never observed any. The insect which fertilizes 

 this species is nearly twice the size of that which performs the same office for 

 P. trullifolia. I have seen an insect enter the flower of P. graminea and 

 become entrapped by the lip. With P. inicrotnega I am imperfectly acquainted, 

 but believe the fertilization to be on the same plan. Of P.foliata I have only 

 seen dried specimens, but as the structure of the flower is in the main the 

 same as in P. trullifolia I have no doubt that it will prove to be fertilized in a 

 similar way. 



It seems hardly necessary to draw attention to the fact that the elaborate 

 structure displayed in this genus is solely used to insure the pollen of one 

 flower being placed on the stigma of a different one. It is not too much to 

 say that the pollinia can never reach the stigma of the same flower, except, 

 perhaps, by a combination of circumstances extremely unlikely to happen. 

 As all our New Zealand species have solitary flowers, the cross effected is not 

 only between different flowers but between different plants. 



Description of Plate XX. 

 Pterostylis trullifolia, Hook. f. Natural size. 



A. Front view of flower. 



B. Lateral view of flower. The sepals and petals on one side removed to 

 show the position of the column and lip. 



