THE EMBRYO 



199 



A 



Tliis type of embryo, called for convenience the Capsella 

 type, is well represented throughout the Dicotyledons, and, so 

 far as we have the means to judge, 

 seems to be the prevalent type, subject, 

 of course, to variation in detail. For 

 example, it occurs in Salix (Chamber- 

 lain 42 ), in which it is questionable 

 whether the hypophysis contributes to 

 the periblem; in Ranunculus (Coul- 

 ter 48 ) and Thalictrum (Overton 83 ), 

 in the latter case the suspensor some- 

 times becoming a massive and twisted 

 organ; in Alyssum (Riddle 51 ), which 

 almost exactly repeats the embryogeny 

 of Capsella; in Sium, in which there 

 is a very long suspensor; in Barcodes 

 (Oliver 3 "); in Avicennia (Treub 24 ); 

 in Trapella (Oliver 21 '), in which there 

 is a remarkably long suspensor with an 

 enormously elongated basal cell ; and in 

 Senecio (Ifottier 34 ), Silphium (Mer- 

 rell 61 ), and Taraxacum (Schwere 40 ). 

 Among the Rosaceae Pechoutre 8T has 

 recorded a wide variation in the struc- 

 ture of the suspensor, different genera 

 showing every gradation between a sim- 

 ple filamentous suspensor (Fragaria, 

 Geum) and one that is short and mass- 

 ive ( Crataegus, Amygdalus). These 

 examples represent all regions of Dicot- 

 yledons ; and while there are differ- 

 ences as to the division of the basal 

 suspensor-cell, the length of the sus- 

 pensor, and the succession of walls in 

 the apical cell (embryo-cell) of trie pro- 

 embryo, the general type remains the 

 same, and resembles most nearly the 

 Alisma type among Monocotyledons. 



In addition to this prevailing type, 

 there are modifications of it that sug- 

 14 



B 



Fio. 91. — Loranthus spftaero- 

 carpus. A, young embryo; 

 >: 190; B, later stage, show- 

 ing extreme lengthening of 

 the two bulbous suspensor- 

 eells ; <?, embryo ; s, suspen- 

 sor ; x 120.— After Tbecb." 



