230 



ESSENTIAL ORGANS — ^POLLEN. 



The term clinandrivm (xXivrj, a bed, and anig, a stamen) is sometimes 

 applied to the part of the column in Orchids where the stamens are 

 situated. 



Fig. 386. 



Pig. 387. 



When mature, the pollen-grain is a cellular body having an exter- 

 nal covering, extine (exto, I stand out, or on the outside), and an 

 internal, intine {inius, within). Fritzsche states that he has detected, 

 in some cases, other two coverings, which he calls intextine and exintine. 

 They occur between the extine and intine, and are probably formed 



Fig. 388. Fig. 389. lit,. "..J. 



by foldings of these membranes. In some aquatics, as Zostera marina, 

 Zannichellia pedunculata, Naias minor, etc., only one covering exists, 



Fig. 385. Flower of Asclepias, showing the poUinia or pollen-masses, p, attached to the 

 stigma, and covered by appendages. Fig. 386. Pistil of Asclepias, a, with poUen-masses, p, 

 adhering to the stigma, s. Pollen-masses, removed from the stigma, &, omited by a gland-like 

 body. Fig. 387. Pollinia or pollen-masses of orchis, separated from the point above the 

 stigma, with their retinacula or viscid matter attaching them at the base. The pollen- 

 masses, p, are supported on stalks or caudicles, c, with glands at base, g. These masses are 

 easUy detached by the agency of insects. Fig. 388. PoUen-grain of Passiflora before burst- 

 ing. 0, Opercula or lids formed by the extine, which open to allow the protrusion of 

 the intine in the form of pollen-tubes. Fig. 389. Pollen-grain of Cucurbita Pepo, or Gourd, 

 at the moment of its dehiscence or rupture, o o, Opercula or lids separated from the extine 

 by the protrusion of the pollen-tubes, 1 1. Fig. 390. Pollen-grain of Ipomcea, with a reticu- 

 lated extine. 



