ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 665 



distinct protuberances and remain distinct throughout from cbalaza to 

 micropyle. In the Amygdaleae two forms occur. In Armeniaca, Persia*, 

 and Amygdalus the initial of the external tegument appears behind that 

 of the internal at a distance of about half the length of an epidermal 

 cell. Only one protuberance is formed, but the two integuments, though 

 in contact, remain distinct throughout. In Cernsus and Prunux the 

 subepidermal cell in which the outer originates immediately precedes 

 the epidermal from which the inner tegument arises. There is a single 

 protuberance in which the two teguments are concrescent ; later, how- 

 ever, the external acquires an epidermis of its own, so that in the 

 micropylar region the two teguments are distinct. In the Spiral both 

 the forms found in Amygdalese occur, while in Spiraea filipendula the 

 concrescence is complete from cbalaza to micropyle. The same com- 

 plete concrescence occurs in the Sanguisorbese (except Alchemilla), in 

 the Roseas aud Rubese. In Alchemilla and in the Potentilleae studied 

 (Geum, Fragaria, Potentilla) except Dryas, where there are two integu- 

 ments, the internal tegument is absorbed, and the ovule is niono- 

 chlamydeous. The subepidermal initial of the outer tegument is 

 beneath the epidermal initial of the inner. Both initials divide at first 

 in the usual way, but the epidermal cells are carried up by the develop- 

 ing external tegument, and are thus prevented from forming an internal. 



The number of layers comprising the two teguments at the time of 

 fertilisation varies considerably from three to ten or more for the outer, 

 and two to four or more for the inner. The time at which the lull 

 number of layers is formed also varies. The seed generally being well 

 protected by the pericarp, and sometimes by a receptacular envelope, the 

 modifications undergone by the ovular integuments in their conversion 

 into seed-coats are generally in the sense of a simplification. In all 

 cases with two teguments the inner takes a part, though a feeble one, 

 in the constitution of the seed-coat, sometimes being represented only 

 by a membranous layer without cellular structure, and never showing 

 any sclerosis. The modifications of the external tegument are subject 

 to numerous variations. There is always a more or less abundant 

 albumen applied to, and intimately united with, the inner face of the 

 seed-coat. 



The sporogenous tissue always arises from several axial sub-epidermal 

 cells, which divide transversely, the upper forming a transitory tapetum, 

 the lower forming the inacrospoie mother-cell, which always divides 

 tiansversely to form three or four daughter-cells, one of which forms 

 the embryo-sac. The primary tapetal cell divides by both transverse 

 and longitudinal walls. In each vertical row all the products of division 

 of the macrospore mother-cell are equivalent in their capacity of forming 

 an embryo-sac. Only one embryo-sac forms in each rank, but several 

 cells belonging to separate ranks may commence development, and one 

 may find in the adult nucellus several perfect embryo-sacs ; generally 

 only a single one arrives at maturity. Any one of the daughter-cells 

 in a series may become the embryo-sac ; the selection depends ap- 

 parently merely on mechanical causes. When one of the upper cells is 

 selected, the lower (generally only one) form anticlinals, which show a 

 higher vitality than their sister cells above the embryo-sac, which early 

 become crushed against the tapetal cells. 



