Chapter XII — 181 — Dionaea and Aldrovanda 



We now direct our attention to certain of the more intimate de- 

 tails of the life history and structure of the plant. 



The seed and seedling (Smith i 931). — The seed is a small pear- 

 shaped mass with a lid at the micropylar end. The embryo, also 

 pear-shaped, Hes with its two broad cotyledons in contact with an 

 abundant endosperm. The cotyledon-ends remain in contact with 

 the endosperm for an extended period, while their bodies enlarge, 

 become green, and eventually spread apart, becoming elongate in 

 form. Meanwhile the primary root has developed, bears a niass of 

 root hairs, but does not persist. From the plumule there arises at 

 once a rhizome bearing small leaves which are similar to the mature 

 leaves in all points, except that they are small (Goebel 1891, Holm 

 1891), the shape of the trap is more rectangular, and the glands 

 are fewer in number. This story, as we shall see, is similar to that 

 of Aldrovanda. 



Although, as Miss Smith says, the juvenile leaves (those of seed- 

 lings) are similar to those of mature plants, there are differences 

 worthy of note, among which are the following: Traps 2 nrni. long 

 have poorly developed marginal spines of rather irregular form and 

 little rigidity, and may arise symmetrically, so that those of the 

 opposing lobes face each other (/5 — 8); or there may be a conspic- 

 uous lack of symmetry and a disparity of number (18 on one side 

 and 13 on the other), some teeth displaying branching to some ex- 

 tent {i8~g). Traps of larger size (4 mm. along the midrib and 7 

 mm. along the free margins) have well developed spines with pos- 

 ture and rigidity comparable to traps on mature leaves. The number 

 of glands in juvenile leaves is much smaller, while the size of the 

 glands approaches that of maturity. They are rather widely scattered. 

 I counted about 70 in the 2 mm. trap {i8~()). There is a wide 

 zone between the outer limit of this glandular region and the lobe 

 margin; and in the outer zone of allure, a narrow zone just within 

 the margin, the nectar (?) glands are only 2 to 12 in number, con- 

 fined to the outer angles of the lobes in the 2 mm. traps examined; 

 while as many as 50 were found in the 4 mm. trap. As would be 

 expected, the structure of the lobes is of much greater delicacy as 

 compared with that of mature leaves. In the 2 mm. trap the lobe 

 was found 0.5 mm. thick at the level of an inner sensitive hair {18 — 

 17, 18). The inner (upper) epidermis cells were somewhat larger than 

 those of the outer in the ratio of 1.4 to i, and had somewhat thicker 

 outer walls. The number of parenchyma cells between ranged from 

 two to four courses with large interspaces, in this feature again re- 

 sembling the mature leaves of Aldrovanda much more than do 

 the thicker mature leaves of Dionaea. It is easier, thus, to see the 

 parallelism of action in these two plants, to which reference is 

 made beyond. The sensitive hairs are much smaller and simpler 

 in construction {18 —t,)- They are about 0.6 mm. long, the outer 

 stiff "lever" being somewhat more than half that. The basal por- 

 tion is deeply constricted, and the bending cells are relatively large 

 and impinge on each other in the middle of the hair, there being 

 no medullary cells. These latter seem, therefore, of no importance 

 beyond that of a filler in the large, sensitive hairs of the mature leaf. 



