■74 SUMMARY OF CURRENT RESEARCHES RELATING TO 



out of the external. The internal are characterized by their diminishing 

 capacity for division, the result being that they passively undergo trans- 

 ference from their original position ; the original connexions between 

 them thereby become lost, and new connecting elements arise which have 

 similar origins but can develop differently according to circumstances. 

 This kind of tissue-formation is repeated at all ages of the plant, and it 

 is only more difficult to recognize in mature plants because of the sub- 

 sequent differentiation of the cells. 3. The haptera appear to be par- 

 ticularly well suited to their function by their growth and multiform 

 shape, as well as by their remarkable capacity for reaction. Their inti- 

 mate blending with the substratum is brought about by the rliizoids, 

 which during germination are developed over the whole base of the 

 plant, but later are formed only on the youngest parts of the holdfasts. 

 4. Other members of the family show more or less complete agreement 

 with the structure of L. digitata, and there are remarkable similarities 

 with the histology of the Fucace^e. 5. L. digitata reacts quickly and 

 actively upon being wounded. The differentiation in stem, frond and 

 haptera, the age and the corresponding specialization of the tissues, 

 necessitate the manifold differences in the regenerated tissues ; also the 

 direction tiud shape of the wound has an influence. 6. As regards the 

 splitting of the frond, for example in L. hyperhorea, one must distinguish 

 between the normal formation and healing which result from an increased 

 growth of the external layer at definite places, and the purely mechanical 

 splitting with its characteristic consequences ; both methods merge into 

 one another. The case appears to be similar in other Laminarias. 7. The 

 Laminarias show for definite ages a definite requirement of light, warmth, 

 salinity, change of water, etc. With the alteration of these conditions 

 are closely connected differences in the external form of the various parts 

 of the thallus and in their character, for example, their strength. The 

 author gives a good bibliography. 



Alternation of Generations in Delesseria sanguinea.* — N. Svede- 

 lius, writing on the developmental history of Delesseria sanguinea, sums 

 up the results of his work as follows. 1. Fertilization takes place in 

 October. Also in October to November the tetrasporophylls begin to 

 appear ; division into tetrads occurs in November, and in December to 

 January both the tetraspores and the cystocarps become mature. 2. The 

 tetrasporangia are normally apical cells arranged in special series, which 

 later become overgrown by neighbouring series of sterile cells, and hence 

 the mature tetrads are embedded. 3. The nucleus of the tetraspore- 

 mother-cell undergoes division into a tetrad preceded by a synapsis and 

 a diakinesis ; in this diakinesis occur twenty double chromosomes. After 

 a heterotypic and homoeotypic division the tetraspore-nuclei with twenty 

 chromosomes are formed. 4. The somatic nuclei of the tetrasporic plants 

 have forty chromosomes, while the somatic nuclei of the female plants 

 have twenty chromosomes. 5. In the resting nuclei is the chromatin 

 divided into numerous chromatin-granules, whose number is somewhat 

 larger than that of the double chromosomes. In the somatic divisions 

 these unite directly into chromosomes without the intervention of a 



* Svensk. Bot. Tidsskr., v. (1911) pp. 260-324 (2 pis and figs.). 



