ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 193 



— which, like themselves, are of endogenous origin — and the exogenous 

 vegetative axes of the plant. 



Degeneration of the Potato.* — G. Delacroix discusses the tendency 

 of potatoes to produce long slender shoots in place of the normal de- 

 velopment. Such tubers when planted show no distinctive characters, 

 and may be softer or harder than usual ; when examined microscopi- 

 cally, there may be found, but not necessarily, Bacillus solanincola, 

 B. caulivorus, and the saprophytic Fusarium Solani. As these or- 

 ganisms may be absent, the abnormal development cannot be caused 

 by them. The true cause rests in the inferior vitality to which many 

 varieties of potato have been reduced as a result of the continued vege- 

 tative and the absence of sexual reproduction. This has reduced to a 

 minimum the power of originating variation, which can therefore only 

 arise in response to the external medium, soil or atmospheric agencies. 

 If the latter are unfavourable, unfavourable characters are induced 

 which become hereditary in successive generations, and the injury by 

 organisms which in the normal state are without effect, becomes possible. 

 Starting the germination of the tuber in the light, will eliminate the 

 slender shoots, and this, followed by a rational culture, serves as a pallia- 

 tive, but the tendency will reappear at the end of several generations. 

 The only certain method of cure is to start from the seed and select 

 carefully. The problem is one not of plant pathology, but of agri- 

 culture. 



Reproductive. 



Development of Gametophyte and Embryo of Ruppia rostellata.f 

 Murbeck has investigated the development of the pollen, the embryo- 

 sac, and the embryo in this form. He finds that in the anther the 

 initials arise as a sub-epidermal layer, and from this layer on the inside 

 the primary archesporial cells are cut off. The pollen-mother-cells show 

 a well-marked synapsis and dolichonema stage in their nucleus, which 

 exhibits eight chromosomes, the vegetative number being sixteen. The 

 cells of the tetrad become separated from one another, and before they 

 are fully developed, each cuts off from one end a small generative cell. 

 By further growth of the pollen-grain the generative cell comes to lie 

 about the middle of the grain near the vegetative cell. Like Potamo- 



i * i 



geton, and the other genera of the Helobieas and Spadicifloraj which 

 have been investigated, the generative- cell divides while the pollen- 

 grains are still in the anther. 



In the ovule a sub-epidermal initial cell appears and cuts off a 

 tapetal cell above which divides to form a single layer of four to six 

 tapetal cells. The lower part becomes the embryo-sac-mother-cell, the 

 nucleus of which soon shows a heterotypic division with synapsis, doli- 

 chonema stage and e^ght chromosomes. The daughter-cells thus formed 

 soon divide again, but the planes of division are not parallel to one 

 another ; the two lower cells of the four being placed under each other, 

 the two upper obliquely side by side. This lends support to the view 

 that the division of the embryo-sac-mother-cell is a tetrad division 



* Comptes Rcndus, cxxxvii. (1903) pp. 1006-7. 



t Bihang. K. Svensk. Vet-Akad. Hand!., xixvi. (1903) pp. 1-21 (3 pi.). 



