114 EMBRYOGENESIS IN PLANTS 



SELAGINELLA KRAUSSIANA, S. POULTERI, S. GALEOTTEI 

 AND S. RUBRICAULIS 



In these species, (Bruchmann, 1912, 1913) the embryogeny shows 

 some curious and interesting developments which are rather different 

 from those described above. 



In S. kraussiana. Fig. 28a-d, the protoplast of the zygote contracts 

 and a new wall is formed round it. It then divides by a transverse wall. 

 Meanwhile the archegonial cavity grows rapidly and penetrates deeply 

 into the prothallus as an elongated tube-like structure (Embryoschlauch), 

 at the inner extremity of which lies the two-celled embryo, Fig. 28a, b. 

 No evident suspensor is formed, its function, as it were, being taken 

 over by the tubular development. In S. galeottei. Fig. 28e-k, there is a 

 somewhat similar development, but in this species the archegonial 

 tube not only penetrates deeply into the prothallial tissue, becoming 

 sinuously curved by the resistance offered to its passage, but it brings 

 about an active disintegration and digestion of the prothallial tissue, 

 Fig. 28g, In this species a suspensor is formed, the pear-shaped zygote 

 dividing by a longitudinal and then by a transverse wall. Fig. 28e-j. 

 In S. poulteri. Fig. 26, the embryo is also thrust deeply into the 

 prothallus, but this is due to a very elongated though infrequently 

 septate suspensor. Fig. 26e. S. nibricaulis is generally like S. galeottei, 

 the developing embryo showing some departure from exact symmetry 

 in its several cell divisions, Fig. 28l. These several species may all 

 develop a more or less considerable foot. 



Bower (1935) has pointed to the variable development of the foot 

 and to the different positions occupied by the first rhizophore in different 

 species. Figs. 25g, 27a, b; 28l. The rhizophore may be formed below 

 the suspensor but on the same side and opposite the foot as in S. 

 denticulata; or opposite the suspensor and above the foot as in 

 S. poulteri; or above the suspensor and foot as in S. galeottei. If we 

 regard the suspensor as of transitory importance only, and the foot as a 

 variable and 'opportunist" growth, the rhizophore is then seen to 

 occupy a normal basal and lateral position relative to the shoot. 



THE CONSTITUTION OF THE APICAL MERISTEM 



Studies of the embryogeny in different species of Selaginella, 

 together with morphological investigation of their development to the 

 adult state, have been productive of interesting facts concerning the 

 histological constitution of the apical meristem (Schiicpp, 1926; Ward- 

 law, 1952). In some species the apical meristems of both shoot and 

 rhizophore may have a definite apical cell, surrounded by its segments 

 which consist of elongated prism-shaped cells; in other species a 



