3io 
R. C. McLean. 
the walls being re-absorbed in the ensuing spring, and the 
radial structure of the true endosperm produced by a process of 
centripetal alveolation in the protoplasmic sac. Strasburger 1 
corrected the erroneous view of there being two successive endo¬ 
sperms, but he confirmed the observation of centripetal alveolation, 
and the resulting radial arrangement of cells. 
The whole process has been fully described, in recent years, by 
Mile. SoIokowa 2 from a number of species of Conifers and Gnetaceae. 
The radial type of structure seems, from her work, to be widely 
distributed among Gymnosperms. In Pinus (sylvestris and pumilio), 
Ceplialotaxus Fortunei, and Ephedra vulgaris, she figures appear¬ 
ances which seem definitely comparable with what occurs in 
Lagenostoma. There is also a radial arrangement in Cunninghamia, 
although the component cells are not elongated. Among the 
Angiosperms, the occurrence of a related type of structure has 
been recorded by Hegelmaier 3 in Adonis. 
The text-figures above illustrate some of the arrangements 
figured by Mile. Solokowa; also the arrangement in Dioon edule, 
after two figures given by Chamberlain. 4 Most of the stages shown 
are fairly young. The radial arrangement tends to become obscured 
in the tissue of less elongated cells which appears secondarily ; 
but this is not so in Araucaria, where it remains perceptible even 
during the development of the embryo, and the same is true of 
Dioon. In all cases the differentiation of a peripheral limiting 
layer of small cells is evident. 
The development of a central plexus in the prothallus is notice¬ 
able both in Araucaria and Lagenostoma. In longitudinal sections 
of the ovule of the recent plant, this plexus is seen to be composed 
of elongated cells forming a broad bundle which presumably 
serves as a means of conduction through the middle of the pro¬ 
thallus. Whether the large development of this tissue in 
Lagenostoma was associated with numerous archegonia, it is impos¬ 
sible to say, the section being cut considerably too low to show 
any trace of those organs. 
The comparison with Araucaria, in spite of the distance 
’ Strasburger. “ Die Angiospermen u. die Gymnospermen.” 
p. 115. 
! Solokowa. Bull, de la Soc. Imp. Nat. de Moscou. Nouv. 
Set*., Tom. IV, 1890. 
3 Hegelmaier. Nova acta d. Kais. Leop. Car. Acad, der 
Naturf, 1885, p. 91. 
* Chamberlain. Bot. Gaz., Vol. 42, 1906. 
