of the Pollen in certain Sweet-Peas. 155 



It appears that in all these plants, the reduction division 

 follows the normal course, and young pollen grains are formed. 

 In the contabescent anthers growth ceases at this point, the pollen 

 grains remain small and enclosed within the walls of the mother- 

 cells. 



* EXPLANATION OF THE FIGURES 



illustrating Grametogenesis in Lathyrus odoratus. 



The figures were drawn with a camera lucida. A Zeiss 2 ram. 

 Apochromatic Objective and Oculars 4, 6, 8, and 18 were used. 



Plate I. 



Fig. 1. Sterile Pea. Pollen-mother-cell in the resting condition. 

 The reticulum is shown, with some threads joining 

 the nucleolus. The latter is somewhat vacuolated, 

 x 1600. 



,, 2. The same. A later stage showing the contraction of the 

 spireme. There are faint indications of the longi- 

 tudinal fission of the thread. The nucleolus has 

 taken a "saucer-shaped" form, x 1600. 



„ 3. " Emily Henderson " (fertile race) ; showing the looping 

 of the thread, which has undergone a complete longi- 

 tudinal fission, x 1600. 



„ 4. Sterile Pea. Nucleus of the embryo sac, in a stage 

 similar to that shown in Fig. 3. x about 2000. 



Figs. 5-8 and 19-20 illustrate sterile plants in which the ab- 

 normality is slight. 



Fig. 5. Sterile Pea. Nucleus of the pollen-mother-cell, showing 

 a later stage, in which the loops are contracted. The 

 longitudinal fission of thread is shown by the di- 

 vergence of the halves in one place. The nucleolus 

 has given up most of its stainable matter, x 1600. 



,, 6. Pollen-mother-cell from the same anther as that shown 

 in Fig. 5. A rather later stage, in which the seg- 

 mentation of the thread into chromosomes has taken 

 place. 



,, 7. Sterile Pea. Pollen-mother-cell from another plant in 

 which the abnormality was slight. The chromosomes 

 appear to be of somewhat different lengths, x 2000. 



,, 8. Two chromosomes from the same, showing the longi- 

 tudinal fission of each limb, x about 2400. 



