194 



MORPHOLOGY OP ANGIOSPERMS 



Fio. 80. — Listera ovuta. 

 Embryo at time of 

 shedding seed. After 

 Pfitzetc in Engler 

 and Prantl's Sat, 

 1'fiiuiZi mfamilien. 



Among the Orchidaceae there is the greatest amount of 

 variation in the formation of the embryo. In general they are 

 characterized by very poorly developed em- 

 bryos, the body regions not being differen- 

 tiated, and by an extraordinary and varied 

 development of the snspensor as an hausto- 

 rivtm. As already mentioned, however, some 

 of them (species of Listera, Epipactis, Good- 

 yera, Spiranthes) have no snspensor (Fig. 



80). Treub 18 in 

 1879 described a 

 number of forms in 

 which the filamen- 

 tous snspensor grows out of the micro- 

 pyle, often branches, and embeds it- 

 self in adjacent nutritive tissue, such 

 as the placenta. He found that in 

 Phalaenopsis grandiflora branches of 

 the snspensor not only turn toward 

 the micropyle, but also toward the 

 embryo and finally envelop it. Later 

 the same investigator 24 described the 

 snspensor of Peristylis grandis as 

 dividing transversely, growing out 

 through the micropyle, and embed- 

 ding itself by pseudopodium-like proc- 

 esses in the placenta. The embryo 

 of Gymnadenia conopsea, as described 

 by Marshall-Ward, 20 is probably rep- 

 resentative. The first division of the 

 fertilized egg is transverse, the basal 

 cell forming a chain-like snspensor of 

 eight to ten more or less elongated 

 cells that pushes through the micro- 

 pyle into the ovary cavity, and the 

 apical cell producing a perfect octant 

 stage, the dermatogen being cut off 

 in the sixteen-celled stage (Fig. 87"). 

 Leavitt 7:! has also described the sus- 

 pensors of Aplectrum hiemale ; of 



Fig. 87. — Gymnadenia conopsea. 

 Section of embryo "with suspen- 

 sor protruding from micropyle. 

 — After Marshall Ward.* 



