32 MORPHOLOGY OF SPERMATOPHYTES 



2. Development of Suspensor. At the beginning of the sec- 

 ond period of development the cavity of the saclike proembryo 

 fills up with tissue somewhat at the base, but is never obliter- 

 ated. This second period, however, is chiefly devoted to the 

 development of the suspensor, which is effected by the elonga- 

 tion of cells in the mass at the base of the spore which lie imme- 

 diately behind the terminal group. These cells, by elongating 

 and dividing, develop a remarkably long and tortuous and mass- 

 ive suspensor, which has never been observed to branch or to 

 give rise to more than a single embryo. The suspensors emerge 

 from the archegonium region in a fascicle, and, imbedded in 

 the endosperm, form a considerable cavity by the disorgan- 

 ization of the adjacent cells. The tips of the suspensors bear- 

 ing the groups of cells destined to form the embryos are im- 

 bedded in the tissues beyond this cavity. The suspensor is 

 quite persistent, remaining attached to the mature embryo, 

 and suspensor coils with abortive embryos may be seen even 

 in ripe seeds. 



3. Development of Embryo. Nothing of morphological sig- 

 nificance is known in reference to the development of the em- 

 bryo. The earliest stages figured show an embryo far advanced. 

 In its complete state the embryo shows two cotyledons, but con- 

 cerning the origin of these cotyledons, or of the stem tip, or of 

 the root tip, we have no information. 



THE SEED 



The seed becomes plumlike, the testa developing from the 

 thick integument, in two layers, the outer fleshy, the inner 

 stony. The view that these two very distinct layers of the testa 

 may represent two integuments, which have been merged into 

 what appears to be a single very thick integument, will be re- 

 ferred to later, in connection with the other groups. In Cycas 

 revoluta, and probably in the other Cycads, the development of 

 the seed does not depend upon fertilization, for with or without 

 pollination there is the same increase in size and development 

 of the two layers of the testa. In germination the cotyledons 

 are said to be hypogean and closely coherent at the apex, as in 

 j but no definite work in seed germination among Cycads 

 seems to have been done. 



